Anatomy Final

Consists of 2 kidneys, 2 ureters, urinary bladder, and urethra

• Filter the blood plasma and excrete the toxic metabolic wastes
• Regulate blood volume, pressure, and osmolarity by regulating water output
• Regulate electrolyte and acid-base blanace of body fluids
• Secrete the hormone erythropoietin, which stimulates the production of red blood cells and thus supports the oxygen-carrying capacity of blood
• Help regulate calcium homeostasis and bone metabolism by participating in the synthesis of calcitriol
• Clear hormones and drugs from the blood and limit their action
• In extreme starvation, they help support the blood glucose level by synthesizing glucose from amino acids

• A waste substance produced by the body
• Nitrogenous wastes

• Most toxic of our metabolic wastes
• Small nitrogen-containing compounds
• 50% is urea, a by-product of catabolism
• Proteins are hydrolyzed to amino acids, and then the -NH2 group is removed from each amino acid
• NH2 is converted into ammonia which the liver quickly turns into urea
• Uric acid and creatinine
• -Produced by the catabolism of nucleic acids and creatine phosphate
• Levels expressed as blood urea nitrogen
• -10-20 mg/dL

• An elevated blood urea nitrogen
• May indicate renal insufficiency
• Can progress to uremia
• Treatment can entail hemodialysis or organ transplant

• A syndrome of diarrhea, vomiting, dyspnea, and cardiac arrhythmia stemming from the toxicity of the nitrogenous wastes
• Convulsions, coma, and death can follow in the next few days

• The process of separating wastes from the body fluids and eliminating them
• Carried out by 4 organ systems
• -Respiratory
• -Integumentary
• -Digestive
• -Urinary

Excretes carbon dioxide, small amounts of other gases, and water

Excretes water, inorganic salts, lactic acid, and urea in sweat

Actively excretes water, salts, carbon dioxide, lipids, bile pigments, cholesterol, and other metabolic wastes

Excretes a broad variety of metabolic wastes, toxins, drugs, hormones, salts, hydrogen ions, and water

• Protected by 3 layers of connective tissue
• Fibrous renal fascia, immediately deep to the parietal peritoneum, binds it to abdominal wall
• Perirenal fat capsule, cushions it and holds it in place
• Fibrous capsule, encloses it anchored at the hilium, and protects it from trauma and infection

• Glandular tissue that forms the urine
• Encircles the renal sinus
• Divided into 2 zones
• -Outer renal cortex
• -Inner renal medlla

• Occupied by blood and lymphatic vessels, nerves, and urine-collecting structures
• Adipose tissue fills the remaining space and holds all of it in place

Has extensions called renal columns that divide the medulla into 6-10 renal pyramids

Receive about 1.2 liters of blood per minute or 21% of the cardiac output

Divides into a few segmental arteries that divide into a few interlobar arteries

• Penetrates each renal column and travels between the pyramids toward the corticomedullary junction
• Branches to form arcuate arteries which give rise to several cortical radiate arteries which give rise to afferent arterioles

• Contains 2 parts
• -Renal corpuscle
• -Renal tubule

• Consists of the glomerulus and a 2-layered glomerular capsule that encloses it
• Outer layer is simple squamous epithelium and inner layer consists of elaborate cells called podocytes
• At opposite side there is a vascular and urinary pole

• Afferent arteriole enters the capsule, bringing blood to the glomerulus
• Efferent arteriole leaves the capsule and carries blood away
• Has a large inlet and small outlet

• Parietal wall of the capsule turns away from the corpuscle, giving rise to the renal tubule
• Simple squamous epithelium becomes simple cuboidal in the tubule

• A duct that leads away from the glomerular capsule
• Divided into 4 regions
• -Proximal convuluted tubule
• -Nephron loop
• -Distal convoluted tubule
• -Collecting duct

• Arises from the glomerular capsule
• Longest and most coiled, therefore dominates histological sections of renal cortex
• Has simple cuboidal epithelium with microvilli
• A lot of absorption occurs here

• Found mostly in the medulla
• Divided into think and thin segments
• Thick segments have a simple cuboidal epithelium and form the intial part of the descending limb and part or all of the ascending limb
• -Active transport of salts, so have high metabolic activity and are full of mitochondria
• Thin segments have a simple squamous epithelium and have a low metabolic activity, but is very permeable to water

• Short and less coiled
• Cuboidal epithelium with smooth-surfaced cells
• End of nephron

• Receives fluid from the DCTs of several nephrons as it passes back into the medulla
• Merge to form a larger papillary duct
• Urine drains from pores into the minor calyx
• Lined with simple cuboidal epithelium

• Just beneath the renal capsule, close to the kidney surface
• Short nephron loops
• Some have no nephron loops at all

• Close to the medulla
• Have very long nephron loops
• Solely responsible for maintaining an osmotic gradient that helps the body conserve water

• Wrapped around each renal artery
• Carries sympathetic innervation from the abdominal aortic plexus and afferent pain fibers
• Stimulation of sympathetic fibers reduce glomerular blood flow, increase rate of urine production, and respond to falling blood pressure by secreting renin

• Converts blood plasma to urine in 4 stages
• -Glomerular filtration
• -Tubular reabsorption
• -Tubular secretion
• -Water conservation

• Similar to blood plasma, but has no protein
• Fluid in the capsule space
• Water and some solutes in the blood plasma pass from capillaries of the glomerulus into the capsular space of the nephron
• Passes through 3 barriers that constitute a filtration membrane
• -Fenestrated endothelium of the capillary
• -Basement membrane
• -Filtration slits

• Endothelial cells have large filtration pores
• Highly permeable
• Pores small enough to exclude blood cells from filtrate

• Has a proteoglycan gel
• Few particles may pepntrate its small spaces, but most would be held back
• Excludes molecules larger than 8nm
• Some particles are held back by a negative charge in the proteoglycan gel
• Has traces of albumin and smaller polypeptides, including some hormones

• A podocyte
• Has a bulbous cell body and several thick arms
• Each arm has little extensions called foot processes
• Have negatively charged to help prevent large anions

• Almost any molecule smaller than 3nm can pass through
• Water, electrolytes, glucose, fatty acids, amino acids, nitrogenous wastes, and vitamins
• Kidney infections and trauma can damage it, allowing albumin or blood cells to filter through

• Blood hydrostatic pressure is much higher here
• Has a larger afferent arteriole and a smaller efferent arteriole
• Hydrostatic pressure of 18mmHg from high rate of filtration and continual accumulation of fluid in capsule
• Colloid osmotic pressure is the same
• Glomerular filtrate is almost protein free

• Ruptures glomerular capillaries and leads to scarring of the kidneys
• Promotes atherosclerosis of the renal blood vessels, thus diminishes renal blood supply
• Often leads to renal failure which leads to worsening of this
• -A positive feedback loop

• The amount of filtrate formed per minute by the 2 kidneys combined
• Males= 125mL/min or 180 L/day
• Females= 105mL/min or 150 L/day
• Average adult reabsorbs 99% of filtrate

• Fluid flows through the renal tubules too rapidly for them to reabsorb the usual amount of water and solutes
• Urine output rises and creates a threat of dehydration and electrolyte depletion

• Fluid flows sluggishly through the tubules
• Reabsorbs wastes that should be eliminated in the urine and azotemia may occur

• The ability of the nephrons to adjust their own blood flow and GFR without external control
• Enables them to maintain a stable GFR in spite of changes in arterial blood pressure
• Helps ensure stable fluid and electrolyte balance
• 2 mechanisms
• -Myogenic mechanism
• -Tubuloglomerular feedback

• Based on the tendency of smooth muscle to contract when stretched
• When arterial blood pressure rises, it stretches the afferent arteriole
• Arteriole constricts and prevents blood flow into the glomerulus from changing very much
• When arterial blood pressure falls, the afferent arteriole relaxes and allows blood to flow more easily into the glomerulus

• The glomerulus receives feedback on the status of the downstream tubular fluid and adjusts filtration to regulate its composition, stabilize nephron performance, and compensate for fluctuations in blood pressure
• Has a structure called the juxtaglomerular apparatus
• 3 Cells
• -Macula densa
• -Juxtaglomerular cells
• -Mesangial cells
• If GFR rises, it increases the flow of tubular fluid and rate of NaCl reabsorption by the PCT

• A patch of slender, closely spaced epithelial cells at the end of the nephron loop on the side facing the arterioles
• If GFR rises, they sense variations in flow or fluid composition and secrete a paracrine messenger that stimulates JG cells

• Enlarged smooth cells in the afferent arteriole
• Directly across from the macula densa
• When stimulated, the dilate or constrict arterioles
• Contain granules of renin, which is secreted in response to a drop in blood pressure
• Initiates the renin-angiotensin-aldosterone mechanism which raises blood pressure

• Cells in the cleft between the afferent and efferent arterioles and among capillaries of the glomerulus
• Connected to the macula densa and JG cells by gap junctions
• Communicate by paracrine secretions
• Build a supportive matrix for the glomerulus, constrict or relax its capillaries to regulate blood flow and GFR, and phagocytize tissue debris

• Richly innervate the renal blood vessels
• In streneous exercise or acute conditions like circulatory shock, stimulation and adrenal epinephrine constrict the afferent arterioles
• Reduces GFR and urine output while redirecting blood from the kidneys to the heart, brain, and skeletal muscles, where it is more needed

• When blood pressure drops because of bleeding, sympathetic fibers stimulate the JG cells to secrete renin
• Renin acts on angiotensinogen to make angiotensin I
• In the lungs and kidneys, angiotensin-converting enzyme removes 2 or more amino acids, converting it to angiotensin II

• Potent vasoconstrictor that raises the mean arterial blood pressure throughout the body
• In kidneys, it constricts the efferent arterioles raising the glomerular blood pressure and GFR
• Stimulates the adrenal cortex to secrete aldosterone, which promotes water reabsorption
• Stimulates posterior pituitary gland to secrete ADH
• Stimulates the sense of thirst and encourages water intake