Chapter 38- Excretory System

Excretion is the ridding of waste products from metabolism.

Osmoregulation is the regulation of solute concentration and water balance by an organism.

Homeostasis is the maintenance of a constant internal environment in an organism.

• 96% water
• Urea - 2%
• Salt
• Traces of other substances (such as hormones)

• Protection
• Vitamin production (D)
• Food storage
• Sense

• Epidermis protects against damage, water loss and the entry if pathogens.
• Melanin protects against ultraviolet radiation.
• Sebum (oil) keeps epidermis intact.

The skin stores energy in fat

The skin senses touch, pain and temperature.

An endotherm is an animal that generates their heat from their own body reactions. Eg. Dogs, humans, elephants.

An ectotherm is an animal that obtains their heat from external sources. Eg. Snakes, lizards, fish.

• Cortex
• Medulla
• Pelvis
• Ureter

• Renal artery
• Afferent arteriole
• Capillaries- Glomerulus (filtration)
• Efferent arteriole - to renal vein
• Bowman’s capsule
• Proximal convoluted tubule (reabsorbtion)
• Loop of Henle (reabsorbtion)
• Distal convoluted tubule (reabsorbtion)
• Collecting duct to the bladder

• Efferent arteriole is narrower than afferent arteriole causing high blood pressure, force filtering plasma.
• Capillaries have large surface area.
• Capillaries have large number of pores.

• A cup-shaped funnel (Bowman’s capsule) surrounds each glomerulus abs it is here that smaller molecules in the blood are forced, under pressure, out of the plasma and into the lumen of the Bowman’s capsule forming glomerular filtrate.
• Glomerular filtrate passes from the Bowman’s capsule into the proximal convoluted tubule.
• Everything except larger molecules enter the glomerular filtrate.

Glomerular filtrate is the plasma with the smaller molecules removed by pressure

• Filtration
• Reabsorbtion
• Secretion

• Filtration: the water and small molecules pass under high pressure from the blood into the nephron
• Renal artery divides into afferent arterioles
• Then divides into a capillary network- glomerulus
• Bowman’s capsule surrounds each glomerulus
• In Bowman’s capsule smaller molecules in the blood are forced, under pressure, out of the plasma and into lumen of Bowman’s capsule, forming the glomerular filtrate.
• (Incl. the 3 ways (/adaptions of) glomerulus helps filtration.)

• Reabsorbtion: molecules pass from the nephron back into the blood.
• Body can’t afford to lose useful chemicals like food and water
• Glomerular filtrate passes from Bowman’s capsule into the proximal convoluted tubule
• Glucose, amino acids, some salts and water are reabsorbed into the blood.
• Food molecules (incl. most salt ions) are taken back against the concentration gradient.
• They’re taken back by active transport
• Most water is reabsorbed by osmosis (loop of Henle and convoluted tubules)

• Secretion: some substances pass from the blood into the nephron.
• Urea, water, some salts and other wastes are not reabsorbed
• Urine passes into the pelvis of the kidney and to the bladder for storage
• Secretion of potassium ions and hydrogen ions into the distal convoluted tubule (highly folded) help maintain the pH of blood.

Anti diuretic hormones control the volume of urine formed by influencing the permeability of the convoluted tubules. It controls osmoregulation, by regulating the amount of water in the body by varying the amount if ur one produced (homeostasis)

• Low fluid content causes salt concentration of plasma to rise
• (If there’s sweating- salt increases)
• Hypothalamus in brain detects this
• Pituitary gland releases ADH
• ADH makes distal convoluted tubule and collecting ducts more permeable
• More water is reabsorbed and less urine is produced
• Salt concentration of plasma falls