Excretion Flashcards
Define excretion
Excretion is the removal of toxic materials and metabolic waste products from the body, via excretory organs
Why is it important to remove nitrogenous and other compound from the body?
Because nitrogenous wastes like creatinine, urea and uric acid they are toxic.
How is urine produced in the urinary system?
- The kidneys receive blood from the renal artery, remove urea and a variable amount of water and mineral salts from it and is returned to the circulation through the renal vein.
- The wastes removed from the blood are eventually excreted in the form of urine from the body through the urethra after being stored in the bladder.
- The kidneys produce urine constantly, high passes to the bladder, via the ureter.
What are the three parts of a kidney?
- Renal cortex: outer portion of the kidney
- Renal medulla: inner portion of the kidney, which consists of a number of renal pyramids
- Renal pelvis: funnel shaped chamber where urine flows from collecting ducts to the ureter
What are the 2 differences between the renal artery and renal vein?
- Walls of renal artery are thicker and more muscular, walls of renal vein are thinner and less muscular
- Semi-lunar valves present in renal vein but not in renal artery
What is the function of a nephron?
The nephron is the functional unit of the kidney. It function to produce urine through ultrafiltration and selective reabsorbtion.
MACRO: what are the organs of the urinary system?
Kidney, ureter, bladder, urethra
MICRO: outline the structure of nephron
A nephron consists of the glomeulus, Bowman’s capsule, afferent and efferent arteriole, proximal convoluted tubule, distal convoluted tubule, loop of Henle, collecting duct and renal venule
Define ultrafiltration
Ultrafiltration is the passage of solutes and water out of glomerulus, drive by the pressure exerted by the blood
Where does ultrafiltration occur?
Renal corpuscle: Bowman’s capsule + glomerulus
How are solutes and water driven out of the glomerulus?
- the diameter of the afferent arteriole is larger than the efferent arteriole
- this creates a high hydrostatic blood pressure in the glomerulus,
- high hydrostatic blood pressure provides the force that drives ultrafiltration
Describe the formation of glomerular filtrate
The glomerulus is a network of capillaries that only allow molecules small enough to pass though into the bowman’s capsule.
The basement membrane of the glomerulus functions like a filter.
Small molecules like water, glucose, amino acids, urea, ions like Na+, Cl- and HCO3- are forced t of the glomerulus into bowman’s capsule, forming the glomerular filtrate.
Large molecules and cells cannot pass through pores in the walls of the glomerulus, eg proteins and fats, blood cells.
Define selective reabsorbtion
Selective reabsorbtion is the selective uptake of solutes and water through processes such as osmosis, active transport, and diffusion.
Where does selective reabsorbtion occur?
It takes place at the proximal convoluted tubule, loop of Henle, distal convoluted tubule and collecting duct.
What substances are/ are not reabsorbed?
- Selectively reabsorbed: some salt, some water
- Entirely reabsorbed: all glucose and amino acids
- Not reabsorbed: urea (bc it is a nitrogenous waste product)
What are the characteristics of he proximal convoluted tubule?
- one cell thick
- many mitochondria, active transport is a key mechanism in reabsorption
- cell surface membrane facing the tubular lumen has microfilm to increase surface area for reabsorption of water and nutrients
- many tight junctions between adjacent cells to prevent substances from diffusing between them
Describe the process of selective reabsorption in the proximal convoluted tubule.
- Na+ is actively transported into the inter- stitial fluid by Na+-K + pump; this is to keep sodium concentration low inside the transport epithelial cells. Na+ diffuses into the transport epithelial cell.
- Glucose and amino acids are co-transported by sodium co-transporter at apical
membrane into the cell; then diffuse out of the epithelial cell down their concentration gradients on passive transporters and are then reabsorbed by the blood capillaries. - Cl- diffuses into the cell because of charge +
5 As salt moves from the filtrate to the interstitial fluid, water follows by osmosis. The salt and water then diffuse from the interstitial fluid into the peritubular capillaries.
gradient set up by active transport of Na ions. - Cl diffuses out of the cell through channels in
the cell wall, and then on into the bloodstream - As salt moves from the filtrate to the interstitial fluid, water follows by osmosis. The salt and water then diffuse from the interstitial fluid into the peritubular capillaries.
Describe the process of selective reabsorption in the descending limb of the loop of Henle
- The loop of Henle creates a high solute (hypertonic) concentration of salts due to the presence of numerous water channel proteins (aquaporins) but are impermeable to sodium ions due to the absence of channel proteins for salts and other small solutes.
- the interstitial fluid nothing the tubule is hyperosmotic to the filtrate; the osmolarity (concentration) of the interstitial fluid increases progressively from the outer cortex to the inner medulla of the kidney.
- hence, as the filtrate flows down the descending limb, reabsorption of after continues and therefore its solute concentration increases.
- water in the medulla is carried away by the vasa recta, thereby maintaining the lower water potential in the medulla
Describe the process of selective reabsorption in the ascending limb of the loop of Henle
- the ascending limb has transport epithelium studded with ion channels, but not water channels. This membrane is impermeable to water.
- the vasa recta blood network that surrounds the loops of Henle flows in the opposite direction (counter-current exchange). This means that salts released from the ascending limb are drawn down into the medulla, further establishing a salt gradient.
What is the function of the distal convoluted tubule?
- It regulates the K+ and NaCl concentrations along with HCO3- of bodily fluids
- the controlled movement of ions contributes to pH regulation
What s the urine composition of a healthy person?
- water, urea, and som mineral salts
Why does a person with diabetes mellitus have glucose in urine?
Diabetics typically have high blood glucose levels, especially after meals.
This results in high glucose concentration in glomerular filtrate during ultrafiltration.
The proximal convoluted tubule is unable to reabsorbed all the glucose.
This results in glucose excreted in urine.
Define osmoregulation
Osmoregulation is the control of water and solute concentrations in the blood to maintain a constant water potential in the blood plasma.
How is ADH produced?
Water potential of blood plasma is monitored by the osmorecpetors in the hypothalamus in the brain. The hypothalamus produces ADH, which is stored and released by the pituitary gland.
