EXAM 4

• Passages that filter incoming air & transport it into the body, into the lungs, and to the many microscopic air sacs where gases are exchanged
• Ventilation (aka, breathing)
• External respiration
• Transport of gases
• Internal respiration
• Cellular respiration

Movement of air in and out of the lungs

Exchange of gases b/t the air in the lungs & the blood

• By the blood
• Between the lungs and body cells

Exchange of gases between the blood and body cells

Utilization of O₂ & production of CO2 by body cells

• Respiration occurs on a macroscopic level at the organ system
• Exchange of the gases O₂ & CO₂ occurs at the cellular & molecular levels

• ATP production
• Carbon dioxide generation

• Energy released when chemical bonds in nutrients are broken
• Electrons are removed from the molecules & channeled through the electron transport chain
• At the end of the chain, the electrons bind to O₂ & H to form H₂O
• Therefore, oxygen is required for these reactions to occur

• Metabolic waste
• Combines with water to form carbonic acid, H₂CO₃, which helps to maintain pH of blood

• Normal breathing is a rhythmic, involuntary act that continues when a person is unconscious
• Respiratory muscles can be controlled voluntarily as well

• Groups of neurons in the brainstem comprise the respiratory areas that control breathing
• Impulses travel on cranial nerves & spinal nerves, causing inspiration and expiration
• Respiratory areas also adjust the rate & depth of breathing to meet cellular needs for supply of O₂ &
• removal of CO₂

• Respiratory center of the medulla
• Respiratory group of the pons
• Additional areas scattered throughout medulla & pons

• 2 bilateral groups of neurons that extend the length of the medulla oblongata:
• Dorsal respiratory group
• Ventral respiratory group

• Stimulate muscles of inspiration, especially the diaphragm
• Increased impulses induce more forceful muscle contractions & greater inspiration
• No impulses cause muscle relaxation & passive expiration

• Control other respiratory muscles, especially the intercostals and abdominals
• During forceful breathing, some neurons increase inspiratory efforts and others increase expiratory efforts

• Located in the pons part of the brainstem
• Make connections with the medullary rhythmicity center
• May contribute to the basic rhythm of breathing

• Number of factors affect breathing rate & depth including:
• Partial pressure of oxygen (Po2)
• Partial pressure of carbon dioxide (Pco2)
• Degree of stretch of lung tissue
• Emotional state
• Level of physical activity

• Receptors:
• Mechanoreceptors
• Central & Peripheral chemoreceptors
• Changes in blood pH, O2 and CO2 concentration stimulates chemoreceptors
• Motor impulses can travel from the respiratory center to the diaphragm and external intercostal muscles
• Contraction of these muscles causes the lungs to expand stimulating mechanoreceptors in the lungs
• Inhibitory impulses from the mechanoreceptors back to the respiratory center prevent overinflation of the lungs

Upper respiratory tract

• The nose
• Nasal cavity
• Sinuses
• Pharynx

• Larynx
• Trachea
• Bronchial tree
• Lungs

• Supported internally by muscle, bone, and cartilage
• Covered with skin
• Nostrils:
• Aka, external nares
• Two
• Openings through which air enters and leaves the nasal cavity
• Many internal hairs guard these openings in order to prevent the entry of large particles that are carried in the air

• Hollow space behind the nose
• Separated into left and right portions by the nasal septum
• Separated from the cranial cavity by the cribriform plate of the ethmoid bone
• Separated frm the oral cavity by the hard palate

• Upper posterior portion of the nasal cavity:
• Slitlike
• Lining contains olfactory receptors
• Remainder of nasal cavity:
• Conducts air to and from the nasopharynx
• Nasal conchae:
• Aka, turbinate bones
• Curl out from the lateral walls of the nasal cavity on each side
• Divide the cavity into passages called the superior, middle & inferior meatuses
• Support the mucous membrane that lines the nasal cavity and helps to increase its surface area

• Pseudostratified ciliated epithelium
• Contains many mucus-secreting goblet cells
• Extensive network of blood vessel
• Pinkish
• Membrane radiates heat from the blood to warm incoming air to body temperature
• Water evaporating from the mucus moistens incoming air
• The sticky mucus entraps dust and other small particles entering with the air
• Cilia of the epithelial cells moves the mucus and particles trapped in it to the pharynx
• The mucus is swallowed from the pharynx
• Microorganisms trapped in the mucus are killed by the gastric juices of the stomach
• Prevents small particles from reaching the lower parts of the respiratory tract and,
• therefore, preventing respiratory infections

• Air-filled spaces in the maxillary, frontal, ethmoid, & sphenoid bones of the skull
• Open into the nasal cavity
• Lined with mucus membranes that are continuous w/ the membranes of the nasal cavity
• Mucus secretions drain into the nasal cavity
• Nasal infections or allergic reactions (sinutis) may cause these tissues to become inflamed or swollen & block drainage
• Blocked drainage increases pressure within the sinuses & causes headaches
• Reduce the weight of the skull
• Act as resonant chambers that affect the quality of the voice

• The pharynx is posterior to the oral cavity and between the nasal cavity and the larynx
• A passageway for air to move b/w the nasal cavity & trachea
• A passageway for food to move from the oral cavity to the esophagus
• Aids in producing sounds from the larynx

• nasopharynx
• oropharynx
• laryngopharynx

• An enlargement in the airway superior to the trachea & inferior to the pharynx
• A passageway for air moving into & out of the trachea
• Prevents large objects from entering the trachea
• Composed of a framework of muscles & cartilages bound by elastic tissue
• Houses the vocal cords
• Large cartilages are single cartilages
• Smaller cartilages are paired

• Thyroid
• Cricoid
• Epiglottic
• All are single

• Arytenoid
• Corniculate
• Cuneiform
• All are paired

• Named for the thyroid gland that covers its lower area
• Hyaline cartilage
• Shieldlike structure that protrudes from the front of the neck
• Sometimes called the Adam’s apple
• Larger in males than females due to effects of male sex hormones on laryngeal development

• Inferior to the thyroid cartilage
• Marks lowermost point of larynx
• Hyaline cartilage

• Only elastic laryngeal cartilage
• Attached to the upper border of the thyroid cartilage & supports the epiglottis
• Epiglottis:
• Usually upright
• Allows air to enter the larynx
• During swallowing, muscular contractions raise the larynx & the base of the tongue presses the epiglottis downward
• Partially covers the opening into the larynx, thus helping to prevent foods and liquids from entering the air passages during swallowing

• Pyramid shaped
• Located superior to and on either side of the cricoid cartilage
• Hyaline cartilage

• Tiny, conelike
• Attached to the tips of the arytenoid cartilages
• Attachments for muscles that help regulate tension on vocal cords during speech and aid in closing the larynx during swallowing
• Hyaline cartilage

• Small, cylindrical structures in the mucous membrane b/t the epiglottis & the arytenoid cartilages
• Stiffen the soft tissues in the area
• Hyaline cartilage

Inside the larynx, two pairs of horizontal folds composed of muscle and connective tissue with a covering of mucous membrane extend inward from the lateral walls

• False vocal cords
• Do not produce sounds
• Help close larynx during swallowing

• Contain elastic fibers
• True vocal cords
• Responsible for vocal sounds, which are created as air forced b/t the folds causes them to vibrate frm side to side

• Air forced through folds of vocal cords produces sound waves
• Sounds formed into words by changing shapes of pharynx & oral cavity and by using tongue and lips
• Pitch (musical tone) controlled by changing tension on vocal cords by contracting or relaxing laryngeal muscles
• Higher tension produces higher pitches
• Intensity (loudness) of sound depends on the force of the air passing over the vocal cords
• Stronger force produces greater vibration of vocal cords & louder sounds

• Normal breathing:
• Vocal cords relaxed
• Glottis, the opening between the vocal cords, is a triangular slit
• Swallowing:
• Muscles close glottis w/in false vocal cords
• Helps prevent food or liquid frm entering trachea along w/ closing of epiglottis and uplift of larynx
• Mucous membrane lining larynx continues to filter incoming air by entrapping particles and moving them toward the pharynx by ciliary action

• Aka, windpipe
• A flexible cylindrical tube abt 2.5 cm in diameter & 12.5 cm in length
• Extends downward anterior to the esophagus and into the thoracic cavity,
• Splits into the right & left primary bronchi in the thoracic cavity

• Inner wall lined with a ciliated mucous membrane that contains many mucus-secreting goblet cells
• Incoming air filtered by cilia
• Entrapped particles moved up trachea to pharynx and swallowed
• About 20 c-shaped pieces of hyaline cartilage within tracheal wall form a column
• Open portion of ring on posterior side of column
• Gaps filled with smooth muscle and connective tissue
• Allow esophagus, located behind trachea, to expand as food passes through it during swallowing
• Rings prevent trachea from collapsing and blocking breathing
• If trachea becomes blocked, asphyxiation occurs w/in min
• Blockage caused by excess secretions, obstruction by a foreign object, or by strangulation
• Tracheostomy opens blocked trachea by creating a temporary external opening in the trachea below the blockage

• The bronchial tree consists of branched airways leading from the trachea to the microscopic air sacs in the lungs
• Trachea forks into right and left primary bronchi at level of the fifth thoracic vertebrae
• Opening of bronchi separated by corina, a ridge of cartilage
• Each bronchus enters its respective lung along w/ large blood vessels

• 1.Right and left primary bronchi
• 2.Secondary or lobar bronchi
• 3.Tertiary or segmental bronchi
• 4.Intralobular bronchioles
• 5.Terminal bronchioles
• 6.Respiratory bronchioles
• 7.Alveolar ducts
• 8.Alveolar sacs
• 9.Alveoli

Three branches from the right and two from the left primary bronchus

• Each branch supplies a bronchopulmonary segment of the lung
• Usually, ten segments in the right lung and eight in the left lung

Enter lobules, the basic units of the lung

50 – 80 per lobule of lung

• Two or more branch from each terminal bronchiole
• Short
• About 0.5 mm in diameter
• Have a few air sacs budding from sides, so they participate in gas exchange

Branch from respiratory bronchioles

Thin-walled, closely packed outpouching of the alveolar ducts

• Thin-walled, microscopic air sacs that open to an alveoloar sac
• Air can diffuse freely frm the alveolar ducts, through the alveolar sacs, & into the alveoli

• Similar to that of the trachea
• C-shaped cartilaginous rings of trachea replaced with cartilaginous plates where the bronchus enters the lung
• Plates irregularly shaped
• Plates completely surround tube
• These respiratory tubes become thinner as they go deeper into the lungs
• Amount of cartilage in the tubes decreases as the tubes become thinner
• Cartilage disappears in the bronchioles
• Layer of smooth muscle surrounds the tubesbeneath the mucosa:
• Increases as the cartilage decreases
• Remains in walls of tubes to ends of respiratory Muscle fibers in the walls of alveolar ducts

• Scattered among smooth muscles cells
• Abundant in connective surrounding tubes
• Important in breathing

• Change as progress to smaller tubes
• Mucous layer thins as progress to smaller tubes
• Larger tubes lined w/ pseudostratified, ciliated columnar epithelial cells & mucus-secreting goblet cells
• As progress to smaller tubes:
• # of goblet cells dec.
• Height of epithelial cells dec.
• Cilia become scarcer
• In respiratory bronchioles:
• Lining becomes cuboidal epithelium
• In alveoli:
• Lining is simple squamous epithelium
• Closely associated with dense network of capillaries
• No mucous lining

• Branches of bronchial tree are passages that filter incoming air and distribute it to alveoli
• Alveoli provide large surface area of thin epithelial cells for gas exchange

• O2 diffuses through alveolar walls and enters blood in nearby capillaries
• CO2 diffuses from the blood, through the alveolar walls, and enters alveoli

• Soft, spongy, cone-shaped organs in the thoracic cavity
• Separated medially by heart and mediastinum
• Enclosed by diaphragm and thoracic (rib) cage
• Each occupies most of the space within its side of thoracic cage
• Suspended by bronchus and large blood vessels
• Tubes enter lung medially through hilum
• Visceral pleura
• Parietal pleura

• A serous membrane that is attached to surface of lung
• Folds back at hilum to become parietal pleura

• Forms part of mediastinum
• Lines inner wall of thoracic cavity

• Between visceral and parietal pleura
• Very little space
• Thin layer of serous fluid:
• Lubricates adjacent pleura
• Reduces friction between pleural layers during breathing
• Helps hold pleural membranes together

• Larger than left lung
• Three lobes separated by fissures
• Called superior, middle, and inferior lobes

• Smaller than right lung
• Two lobes separated by a fissure
• Called superior and inferior lobes

• Each supplied by a lobar bronchus
• Has connections to blood & lymphatic vessels
• Each enclosed in connective tissues
• Divided into lobules:
• Separated by connective tissue
• Each contains terminal bronchioles with their alveolar ducts, alveolar sacs, alveoli, nerves, and associated blood and lymphatic vessels

• Dome-shaped muscle
• Located just inferior to lungs
• Anterior group of skeletal muscle fibers:
• Costal fibers
• Originate from ribs and sternum
• Posterior group of skeletal muscle fibers:
• Crural fibers
• Originate from vertebrae
• Both groups of fibers insert on tendinous central portion of diaphragm
• Stimulated to contract by impulses carried by the phrenic nerves

• Breathing, aka ventilation
• Movement of air from outside of the body into the bronchial tree and the alveoli:
• Called inspiration, aka inhalation
• Reversal of this movement:
• Called expiration, aka exhalation

• Atmospheric pressure due to the weight of the air is the force that moves air into the lungs
• At sea level, atmospheric pressure is 760 millimeters of mercury (mm Hg)
• Air pressure exerted on all surfaces in contact with air, including internal surfaces of lung
• When respiratory muscles are at rest, the pressures on the inside of the lungs and alveoli and on the outside of the throacic wall are about equal

• Pressure and volume are inversely proportional
• EX: Syringe
• Pulling the plunger back in a syringe
• Increases the volume within the syringe
• Decreases the pressure of the air within the syringe
• Atmospheric pressure pushes air into the syringe in order to equalize the pressure inside and outside the syringe
• Pushing the plunger into a syringe:
• Increases the volume within the syringe
• Decreases the pressure of the air within the syringe
• Atmospheric pressure pushes air into the syringe in order to equalize the pressure inside and outside the
• syringe

• Diaphragm & external intercostal muscles contract more forcefully
• Pectoralis minor and sternocleidomastoids can contract to pull thoracic cage outward and upward
• More forceful and additional muscle contractions further increase the size of the thoracic cavity and decrease the inter-alveolar pressure so more air is inspired

• Aka, distensibility
• Ease w/ which lungs expand as a result of pressure changes during breathing
• Normal lung:
• Compliance decreases as lung vol. inc. b/c an inflated lung is harder to expand than one at rest
• Dec. by conditions that obstruct air passages, destroy lung tissue, or otherwise impede lung expansion

• The forces responsible for normal resting expiration come frm elastic recoil of lung tissues & frm surface tension
• Diaphragm and external intercostal muscles relax after inspiration
• Recoil of elastic fibers in lung tissues reduces pressure in pleural cavity to about 4 mm Hg below atmospheric pressure

• Posterior internal (expiratory) intercostal muscles contract
• Pull ribs and sternum downward and inward
• Increase pressure in the lungs
• Abd wall muscles inc. the pressure in the abd cavity & force the diaphragm to push higher against the lungs

• Occurs when the thoracic wall is punctured
• Air may enter thoracic cavity & separate visceral & parietal pleural membranes
• Lung may collapse on same side of body
• Lung reinflated by inserting a tube into the thorax & pulling a vacuum while preventing air from reentering the thorax around the opening

• Diff degrees of effort in breathing move different vol of air in & out of the lungs
• Spirometry:
• Measurement of air volumes during breathing
• Four respiratory volumes
• Respiratory cycle = one inspiration and the following expiration
• Measurement made using a spirometer
• Used to measure course of respiratory illnesses & breathing abilities of endurance athletes

• Tidal volume
• Inspiratory reserve volume
• Expiratory reserve volume
• Residual volume

• Vol of air that enters or leaves during a respiratory cycle
• Normally, about 500 ml for a tall young man who is resting
• Resting tidal volume describes tidal volume when person is & has been resting quietly

• Volume of air entering lungs in addition to tidal volume during forced maximal inspiration
• Normally, 3000 ml

• Volume of air leaving lungs in addition to tidal volume during max forceful expiration
• Normally, 1000 ml

• Vol of air remaining in lungs after maximal forceful expiration
• Normally, 1200 ml
• Not measured with a spirometer

• Vital capacity
• Inspiratory capacity
• Functional reserve capacity
• Total lung capacity

• Maximum volume of air that can be expelled after taking the deepest breath possible
• =Tidal volume + inspiratory reserve volume + expiratory reserve volume

• Max vol of air that can be inhaled following a resting expiration
• = Tidal volume + inspiratory reserve volume

• Vol of air remaining in the lungs following a resting expiration
• = Expiratory reserve volume + residual volume

• Total air volume in the lungs after maximal inspiration
• = Vital capacity + residual volume
• Varies with age, sex, and body size

• Anatomic dead space:
• Occupied by air remaining in passageways after inspiration
• This air not used for gas exchange
• Alveolar dead space:
• Occupied by air in air sacs that are not functional due to poor blood flow in adjacent capillaries
• This air not used for gas exchange
• Physiologic dead space:
• Occupied by air that is not used for gas exchange
• = Anatomic dead space + Alveolar dead space
• Residual air remains in the lung at all times
• Mixes with newly inhaled air preventing concentrations of O2 and CO2 from varying too much during each breath

• Minute ventilation
• = Volume of new atmospheric air moved into the respiratory passages each minute
• = Tidal volume multiplied by the breathing rate
• Much of the new air remains in the physiologic dead space
• Vol of new air that reaches the alveoli & is available for gas exchange is calculated by subtracting the physiologic dead space from the tidal volume
• Alveolar ventilation rate:
• = The tidal volume minus the physiologic dead space then multiplied by the breathing rate
• This impacts the concentrations of O2 & CO2 in the alveoli

• Air movements other than breathing are called nonrespiratory movements
• They clear air passages, as in coughing and sneezing, or express emotions, as in laughing and crying
• Usually result from reflexes, although they are sometimes initiated voluntarily

• Taking a deep breath, closing the glottis, forcing air upward from the lungs against the closed glottis
• Then the glottis is opened suddenly and a blast of air is forced upward from the lower respiratory tract
• Usually the rapid rush of air removes the substance that triggered the reflex
• No sensory nerves in the lower respiratory tract, so materials in these areas must be moved by mucus to larger areas before they can be expelled

• Similar to coughing
• Clears upper respiratory passages
• Usually initiated by mild irritation in the nasal cavity
• Blast of air forced up through the glottis
• Air directed into nasal passages by deptessing the uvula, thus closing the opening between the pharynx & the oral cavity

• A deep breath taken
• Air released in short expirations

• Similar movements to laughing
• May need to look at person’s face to distinguish b/t laughing & crying

• Caused by a sudden inspiration due to a spasmodic contraction of the diaphragm while the glottis is closed
• Sound caused by air striking the vocal folds
• Function unknown

• Significance and mechanism of contagion are poorly understood
• In past, believed to have a role in increasing oxygen intake
• May be rooted in primitive brainstem mechanisms that maintain alertness

Sites of the vital process of gas exchange b/t the air & the blood

• Part of the wall of an alveolus is made up of cells (type II cells) that secrete pulmonary surfactant
• The bulk of the wall of an alveolus consists of a layer of simple squamous epithelium (type I cells)
• Both of these layers make up the respiratory membrane through which gas exchange takes place

• Molecules diffuse from regions where they are in higher concentration toward regions where they are in lower concentration
• It is important to know the concentration gradient
• In respiration, think in terms of gas partial pressures
• Gases diffuse from areas of higher partial pressure to areas of lower partial pressure
• The respiratory membrane is normally thin and gas exchange is rapid
• Increased diffusion is favored with more surface area, shorter distance, greater solubility of gases and a steeper partial pressure gradient
• Decreased diffusion occurs from decreased surface area

• Blood transports O2 & CO2 between the lungs
• & the body cells
• As the gases enter the blood, they dissolve in the plasma or chemically combine with other atoms or molecules

• Almost all O₂ carried in the blood is bound to the protein hemoglobin in the form of oxyhemoglobin
• Chemical bonds between O2 & hemoglobin are relatively unstable
• Oxyhemoglobin releases O2 into the body cells
• About 75% of the O2 remains bound to hemoglobin in the venous blood ensuring safe CO2 levels and thereby pH

• Blood flowing through capillaries gains CO2 b/c the tissues have a high Pco2
• The CO2 is transported to the lungs in one of three forms:
• As CO2 dissolved in plasma
• As part of a compound with hemoglobin
• As part of a bicarbonate ion

• A major part of homeostasis is maintaining the composition, pH, and volume of body fluids within normal limits
• The urinary system removes metabolic wastes & substances in excess, including foreign substances like drugs & their metabolites that may be toxic

• Pair of kidneys
• Pair of ureters
• Urinary bladder
• Urethra

• Reddish brown, bean-shaped organ w/ a smooth surface
• Located on either side of the vertebral column
• In a depression high on the posterior wall of the abdominal cavity
• Upper and lower boundaries generally at the levels of the twelfth thoracic and third lumbar vertebrae,
• respectively
• Position changes slightly with posture and breathing movements
• Left kidney usually 1.5 – 2 cm higher than right kidney

Behind the parietal peritoneum

• Against deep muscles of the back
• Connective tissue (renal fascia) and masses of adipose tissue (renal fat) hold them in place
• In the adult they are about 12 centimeters long, 6 cm wide, & 3 cm thick
• Enclosed in a tough, fibrous capsule
• Glandular
• Remove substances from blood
• Form urine
• Help regulate certain metabolic processes

• Lateral surface is convex
• Deeply concave
• Medial depression leads to a hollow cave called the renal sinus
• Entrance to the sinus is the hilum
• Blood vessels, lymph vessels, nerves, and ureter pass through the hilum

• Expanded portion of ureter forming a funnel-shaped sac
• Located at the superior end of ureter
• Subdivided into 2 – 3 tubes called major calyces
• Each major calyx subdivided into 8 – 14 minor calyces
• Renal papilla is a small projection extending into each minor calyx

• Renal medulla
• Renal cortex

• Inner region
• Composed of conical masses called renal pyramids
• Bases orient toward convex surface of kidney
• Apexes form renal papillae
• Tissue appears striated due to microscopic tubules leading from the cortex to the renal papillae

• Appears somewhat granular
• Forms a shell around medulla
• Tissue extends into medulla b/t renal pyramids to form renal columns

• Fibrous membrane surrounding renal cortex
• Helps maintain shape of kidney
• Helps protect kidney

• The main function of the kidneys is to regulate the vol, composition, and pH of body fluids
• Remove metabolic wastes from the blood & excrete them to the outside of the body, including nitrogenous & sulfur-containing products of protein metabolism
• The rate of red blood cell production by secreting the hormone erythropoietin
• Regulate blood pressure by secreting the enzyme renin
• Regulate calcium ion absorption by activating vitamin D

• Substitutes for role of kidney
• Blood rerouted across an artificial membrane that removes substances that would normally be removed in the kidney
• Usually done for several hours three days a week
• In some patients, may be replaced by continuous ambulatory peritoneal dialysis
• A solution infused into patient’s peritoneum through a permanently implanted tube
• After 4 – 8 hours the solution is removed & replaced w/ more solution
• Solution takes up substances that would normally be excreted in urine

• The main function of the nephrons and collecting ducts is to control the composition of body fluids and remove wastes from the blood, the product being urine
• Urine contains wastes, excess water, and electrolytes
• Urine is the final product of the processes of:
• Glomerular filtration
• Tubular reabsorption
• Tubular secretion

The main force that moves substances by filtration through the glomerular capillary wall is hydrostatic pressure of the blood inside

• Glomerular filtration rate (GFR) is directly proportional to the net filtration pressure
• Normally the glomerular net filtration pressure is positive causing filtration
• The forces responsible include hydrostatic pressure & osmotic pressure of plasma and the hydrostatic pressure of the fluid in the glomerular capsule

• GFR remains relatively constant through a proces called autoregulation
• Certain conditions override autoregulation, including when GFR increases

• Autoregulation
• Increased sympathetic impulses that decrease GFR by causing afferent arterioles to constrict
• The hormone-like renin-angiotensin system
• There also is the hormone atrial natriuretic peptide (ANP) affects sodium causing an increase in GFR

Tubular reabsorption

• Substances move from the renal tubules into the interstitial fluid where they then diffuse into the peritubular capillaries
• The proximal convoluted tubule reabsorbs (70%):
• Glucose, water, urea, proteins, and creatine
• Amino, lactic, citric, and uric acids
• Phosphate, sulfate, calcium, potassium, and sodium ions

• Substances move from the plasma of the peritubular capillaries into the fluid of the renal tubules
• Active transport mechanisms function here
• Secretion of substances such as drugs and ions

• Hormones such as aldosterone and ANP affect the solute concentration of urine, particularly sodium
• The ability of the kidneys to maintain the internal environment rests in a large part on their ability to concentrate urine by reabsorbing large volumes of water
• The distal convoluted tubule and the collecting duct are impermeable to water, so water may be excreted as dilute urine
• If ADH is present, these segments become permeable, and water is reabsorbed by osmosis into the extremely hypertonic medullary interstitial fluid
• A countercurrent mechanism in the nephron loops (the descending and the ascending limbs) ensures that the medullary interstitial fluid becomes hypertonic
• This mechanism is known as the countercurrent multiplier
• The vasa recta also contributes as a countercurrent mechanism

• A by-product of amino acid catabolism
• The plasma concentration reflects the amount of protein in diet
• It enters the renal tubules through glomerular filtration
• It contributes to the reabsorption of water from the collecting duct
• About 80% is recycled

• Is a product of nucleic acid metabolism
• It enters the renal tubules through glomerular filtration
• Most reabsorption occurs by active transport
• About 10% is secreted and excreted

• Urine composition reflects the volumes of water and solutes that the kidneys must eliminate from the body or retain in the internal environment to maintain homeostasis
• It varies from time to time due to dietary intake and physical activity, but is:
• About 95% water
• Usually contains urea, uric acid, and creatinine
• May contain trace amounts of amino acids and varying amounts of electrolytes
• Volume varies with fluid intake and environmental factors

• This is the rate at which a chemical is removed from the plasma
• It indicates kidney efficiency
• Tests of renal clearance:
• Inulin clearance test
• Creatinine clearance test
• Para-aminohippuric acid (PAH) test
• These tests of renal clearance are used to calculate the GFR (glomerular filtration rate)

• After forming along the nephrons, urine:
• Passes the collecting ducts to:
• Openings of the renal papillae:
• Enters the minor and major calyces:
• Passes through the renal pelvis:
• Enters into the ureters:
• Enters into the urinary bladder:
• The urethra carries the urine out of the body

• Each is about 25 centimeters long
• Extends downward posterior to the parietal peritoneum
• Runs parallel to vertebral column
• Join the urinary bladder in the pelvic cavity
• Tubular
• Transport urine from the kidneys to the bladder

• The inner mucous coat
• The middle muscular coat
• The outer fibrous coat

• The urinary bladder is a hollow, distensible, muscular organ located within the pelvic cavity, posterior to the symphysis pubis and inferior to the parietal peritoneum
• It contacts the anterior walls of the uterus and vagina in the female, and lies posteriorly against the rectum in the male
• The openings for the ureters is the area of trigone
• Saclike
• Urine reservoir

• Inner mucous coat
• Submucous coat
• Muscular coat
• Outer serous coat
• Urine leaves the urinary bladder by micturition or urination reflex

Urine leaves the urinary bladder by micturition or urination reflex

• The urinary system is sufficiently redundant, in both structure and function, to mask age-related changes
• The kidneys become slower to remove nitrogenous wastes and toxins and to compensate for changes that maintain homeostasis
• The kidneys appear scarred and grainy
• Kidney cells die
• By age 80 the kidneys have lost a third of their mass
• Kidney shrinkage is due to loss of glomeruli
• Proteinuria may develop
• The renal tubules thicken
• It is harder for the kidneys to clear certain substances
• The bladder, ureters, and urethra lose elasticity
• The bladder holds less urine

• The term balance suggests a state of equilibrium
• For water and electrolytes balance means equal amounts enter and leave the body
• Mechanisms that replace lost water and electrolytes and excrete excesses maintain this balance
• These mechanisms result in stability of the body at all times
• Water and electrolyte balance are interdependent because electrolytes are dissolved in the water of body fluids
• Anything that alters the concentration of electrolytes also alters the concentration of water by adding solutes to it or removing
• solutes from it
• Anything that alters the concentration of water alters the concentration of electrolytes by concentrating or diluting them

• Body fluids are not uniformly distributed
• They occupy compartments of different volumes that contain varying compositions
• Water and electrolyte movement between these compartments is regulated to stabilize their distribution and the composition of body fluids

• Intracellular fluid
• Extracellular fluid

Includes all water and dissolved electrolytes enclosed in cell membranes

• Includes all fluids outside of cells
• Interstitial fluids in tissue spaces
• Plasma in blood vessels
• Lymph in lymphatic vessels
• Transcellular fluids
• A specialized fraction of extracellular fluid separated from other extracellular fluids by epithelial tissue layers
• Includes cerebrospinal fluid of the central nervous system, aqueous and vitreous humors of the eyes, synovial fluid of the joints, serous fluid within the body cavities, and fluid excretions of endocrine glands

• Of the 40 liters of water in the body of an average adult, about two-thirds is intracellular fluid and one-third is
• extracellular fluid
• An average adult female is about 52% water by weight, and an average male about 63% water by weight
• Females have more fat, which contains little water
• Males have more muscle, which contains much water

• Hydrostatic pressure
• Osmotic pressure

• Outward force at arteriolar end of capillaries
• Inward force into lymph vessels

• Inward force at venular end of capillaries
• Net movement of water between interstitial fluid and intracellular fluid
• Hydrostatic pressure usually equal and stable between these fluids so osmotic pressure is primarily responsible for movement of water
• Extracellular sodium ions and intracellular potassium ions are impermeant solutes in the absence of transport by a Na+/K+ pump so they drive osmosis
• Decreased extracellular sodium ion concentration makesextracellular fluid hypotonic (less concentrated) compared to intracellular
• fluid so water enters cells, which swell, so solute concentrations become equalized
• Increased extracellular sodium ion concentration, cells lose water and shrink as water moves out of the cell and into intercellular
• fluid
• Although solute composition of body fluids varies between intracellular and extracellular compartments, water follows the salt and is
• distributed by osmosis such that the water concentration and total solute concentration are essentially equal inside and outside of the cells

• Exists when water intake equals water output
• Homeostasis requires control of both water intake and water output
• Maintenance of the internal environment depends on thirst centers in the brain to vary water intake and on the kidneys’ ability to vary water output

• The volume of water gained each day varies among individuals averaging about 2,500 milliliters daily for an adult:
• 60% from drinking
• 30% from moist foods
• 10% as a bi-product of oxidative metabolism of nutrients called water of metabolism

• Primary regulator of water intake is thirst
• Usually triggered by as little as a 1% decrease in total body water
• Feeling of thirst derives from the osmotic pressure of extracellular fluids and a thirst center in the hypothalamus
• As the body loses water, the osmotic pressure of extracellular fluids increases
• Increased osmotic pressure stimulates osmoreceptors in the thirst center
• Hypothalamus causes person to feel thirsty and to seek water
• A thirsty person usually has a loss of extracellular water and a concomitant decrease in flow of saliva resulting in a dry mouth
• Distension of the stomach after drinking water triggers nerve impulses that inhibit the thirst mechanism
• Thirst is quenched and drinking stops before the water is absorbed in order to prevent overconsumption of water and a water imbalance in the opposite direction

• Water normally enters the body only through the mouth, but it can be lost by a variety of routes including:
• Urine (60% loss)
• Feces (6% loss)
• Sweat (sensible perspiration) (6% loss)
• Evaporation from the skin (insensible perspiration)
• The lungs during breathing
• (Evaporation from the skin and the lungs is a 28% loss)
• The percentages vary with environmental factors such as temperature, relative humidity, and with physical activity
• If water intake is too low, then water output must be decreased to maintain balance
• Primary means of controlling water output is to control urination
• Other means of water loss can’t change much due to their other functions in the body
• Sweating is an essential part of controlling body temperature
• Water loss in feces accompanies undigested food materials and doesn’t change significantly
• Water loss by evaporation is largely unavoidable

• Distal convoluted tubules & collecting ducts of nephrons regulate volume of water excreted in urine
• Epithelial linings of these parts of the renal tubule are relatively impermeable to water except in the presence of antidiuretic hormone (ADH)
• Osmoreceptors in the hypothalamus help control release of ADH

Change causes hypothalamus to send signals to posterior pituitary gland to release ADH into the bloodstream

ADH increases permeability of distal convoluted tubules and collecting ducts

Resulting increased water reabsorption conserves water & resists further osmotic change in the plasma

Can reduce urine output by 2/3

• Release of ADH from the posterior pituitary gland is inhibited by signals from the hypothalamus
• Distal tubules and collecting ducts remain impermeable to water
• More water is reabsorbed
• Less urine is produced

An electrolyte balance exists when the quantities of electrolytes (molecules that release ions in water) the body gains equals those lost

• The electrolytes of greatest importance to cellular functions release Na, K, Ca, Mg,
• Cl, S, Ph, bicarbonate, & H ions
• Obtained from foods, but some are from water & other beverages
• Some electrolytes are by-products of metabolic reactions

• Ordinarily, a person obtains sufficient electrolytes by responding to hunger and thirst
• A severe electrolyte deficiency may cause salt craving

• The body loses some electrolytes by perspiring
• Typically occurs on warmer days and during strenuous exercise
• Sweat has about half the concentrations of solutes as blood plasma does
• Quantity of electrolytes lost depends on amount of sweat
• Varying amounts are lost in the feces
• The greatest output is as a result of kidney function & urine output
• Kidneys change amount of electrolytes excreted to maintain proper electrolyte composition of body fluids

• Molecules that are polar or have polar regions within them dissolve in water but remain intact
• Molecules that are held together by ionic bonds, such as electrolytes, dissociate in water to release ions

• Osmolarity of body solutions determined by the total # of dissolved particles irrespective of their source
• Unit of osmolarity is osmoles/liter
• Osmoles are determined by the total number of dissolved particles
• Glucose remains intact, so 1 mole
• glucose gives one osmole of dissolved particles
• Sodium chloride breaks into two
• ions, so 1 mole NaCl gives two osmoles of dissolved particles

• Nearly 90% of the positively charged ions in extracellular fluids
• Kidney and aldosterone provide primary mechanism of regulating sodium ion concentration
• Aldosterone secreted by the adrenal cortex increases reabsorption of sodium ions in the distal convoluted tubules and collecting ducts of the
• kidney
• Decreased sodium ion concentration in extracellular fluid stimulates aldosterone secretion by the renin angiotensin system

• Especially important in maintaining the resting potential of nerve and cardiac muscle cells
• Abnormal levels may cause these cells to function abnormally
• Regulated by aldosterone
• Rising potassium ion concentration directly stimulates the adrenal cortex to secrete aldosterone
• Aldosterone enhances renal tubular reabsorption of sodium ions and stimulates renal tubular secretion of potassium ions

• Low calcium ion concentration directly stimulates parathyroid gland to secrete parathyroid hormone (PTH)
• PTH increases activity of bone-resorbing cells (osteoblasts and osteocytes)
• Increases concentration of both calcium & phosphate ions in extracellular fluids
• PTH indirectly stimulates calcium absorption from the intestine
• PTH causes kidneys to conserve calcium ions by increased tubular reabsorption
• PTH causes kidneys to increase urinary excretion of phosphate ions
• Increased phosphate excretion offsets increased plasma phosphate
• Net effect of PTH is to return the calcium ion concentration of extracellular fluids to normal levels & to maintain a normal phosphate ion concentration
• Negatively charged ions
• Regulatory mechanisms that control positively charged ions generally have a secondary effect of regulating the concentrations of negatively charged ions

• Most abundant negatively charged ions in extracellular fluid
• Passively reabsorbed from renal tubules in response to the active reabsorption of sodium ions
• Electrically attracted to positively charged sodium ions & accompany the sodium ions as they are reabsorbed
• Some partially regulated by active transport mechanisms that have limited capacities
• Includes phosphate and sulfate
• ions
• If the extracellular concentration of phosphate ions is low, the phosphate ions in renal tubules are
• conserved
• If the renal plasma threshold for phosphate ions is exceeded, the excess phosphate ions are excreted in the urine

• Electrolytes that ionize in water and release hydrogen ions are acids
• Substances that combine w/ hydrogen ions are bases
• Acid-base balance entails regulation of the hydrogen ion concentrations of body fluids
• Important because slight changes in hydrogen ion concentrations can alter the rates of enzyme controlled metabolic reactions, shift the distribution of other ions, or modify hormone actions
• The degree to which a solution is acidic or basic is represented by a pH number
• The lower the pH, the more hydogen ions are in the solution and the more acidic the solution is
• pH of the normal internal environment is 7.35 – 7.45

• Most hydrogen ions in body fluids originate as by-products of metabolic processes
• Small quantities may be absorbed directly from the digestive tract
• The reactions are reversible, but the pH is determined by the concentration of hydrogen ions at equilibrium

• Aerobic respiration of glucose
• Anaerobic respiration of glucose
• Incomplete oxidation of fatty acids
• Oxidation of amino acids containing sulfur
• Hydrolysis (breakdown) of phosphoproteins & nucleic acids

• Produces CO2 and H2O
• CO2 diffuses out of cells and reacts with water in the extracellular fluid to produce carbonic acid
• CO2 + H2O → H2CO3
• Carbonic acid ionizes to release hydrogen ions & bicarbonate ions

Anaerobic respiration of glucose produces lactic acid, which ionizes to release hydrogen ions to body fluids

Produces acidic ketone bodies, which increase hydrogen ion concentration

Produces sulfuric acid, H2SO4, which ionizes to release hydrogen ions

• Both contain phosphorus
• Oxidation of both produces phosphoric acid, H3PO4, which ionizes to release hydrogen ions

• Strong acids ionize more completely and release more H+
• HCl in gastric juice is a strong acid
• Completely dissociates in water to release much H+
• Weak acids ionize less completely and release fewer H+
• Carbonic acid is a weak acid
• Does not completely dissociate in water, so it releases fewer H+

• Release ions such as OH- which can combine with H+ to lower their concentration & raise the pH
• Strong bases ionize more completely and release more OH-
• NaOH is a strong base and dissociates completely
• Weak bases ionize less completely and release fewer OH-
• Sodium bicarbonate is a weak base and releases fewer negative ions
• The bicarbonate ion is called a weak base
• The bicarbonate ion combines with H+ to produce the weak acid carbonic acid

• Either an acid shift or an alkaline (basic) shift in the body fluids could threaten the internal environment
• Normal metabolic reactions generally produce more acid than base
• The reactions include cellular metabolism of glucose,
• fatty acids, and amino acids

• Acid-base buffer systems
• Respiratory excretion of carbon dioxide
• Renal excretion of hydrogen ions

• In all body fluids
• Based on chemicals that bind with excess acids or bases
• Buffers are substances that stabilize the pH of solution, even when acids or bases are added
• Components can combine with strong acids to make weak bases or with strong bases and make them weak acids
• Function to minimize pH changes in the body fluids

• Bicarbonate buffer system
• Phosphate buffer system
• Protein buffer system

• Present in both intracellular and extracellular fluids
• The bicarbonate ion acts as a weak base
• The bicarbonate ion combines with excess hydrogen ions released by strong bases
• The bicarbonate ion converts a strong acid to a weak acid
• Although free bicarbonate ion is released, the increase of free hydrogen ions at equilibrium that minimizes the shift to a higher pH
• Carbonic acid converts a strong base to a weak base H+ + HCO3- à H2CO3 à H+ + HCO3-

• Present in both intracellular and extracellular fluids
• Especially important in controlling H+ concentration in intracellular fluid and in renal tubular fluid and urine
• Consists of two phosphate ions
• Dihydrogen phosphate, H2PO4-
• Monohydrogen phosphate, HPO4-2
• The monohydrogen phosphate ion acts as a weak base
• The monohydrogen phosphate ion converts a strong acid to a weak acid
• The dihydrogen phosphate ion acts as a weak acid
• The dihydrogen phosphate ion converts a strong base to a weak base H+ + HPO4-2 à H2PO4- à H+ +
• HPO4-2

• Consists of the plasma proteins, such as albumins, & certain proteins within cells, such as hemoglobin
• Some amino acids have freely exposed carboxyl groups, COOH
• If the H+ concentration decreases, a carboxyl group releases a H+
• NH3+ group releases a hydrogen ion in the presence of excess base
• COO- group accepts a hydrogen ion in the presence of excess acid

• The respiratory center in the brainstem helps regulate hydrogen ion concentrations in the body fluids by controlling the rate and depth of breathing
• If body cells increase their production of CO2

Nephrons help regulate the hydrogen ion concentration of body fluids by excreting hydrogen ions in the urine

• Various regulators of hydrogen ion concentration operate at different rates
• Acid-base (chemical) buffers function rapidly
• Respiratory and renal (physiological buffers) mechanisms function more slowly

• Chemical and physiological buffer systems ordinarily maintain the hydrogen ion concentration of body fluids within very narrow pH ranges
• Abnormal conditions may disturb the acid-base balance

• Acidosis results from the accumulation of acids or loss of bases, both of which cause abnormal increases in the hydrogen ion concentrations of body fluids
• Alkalosis results from a loss of acids or an accumulation of bases accompanied by a decrease in hydrogen ion concentrations

• Respiratory alkalosis develops as a result of hyperventilation
• Metabolic alkalosis results from a great loss of hydrogen ions or from a gain in bases, both accompanied by a rise in the pH of blood