1. © SSER Ltd.

2. The principal functions of the kidneys are:
The Mammalian Kidney
The principal functions of the kidneys are:
Excretion – removal of toxic nitrogenous waste products of metabolism; these include urea and creatine (a waste product of muscle metabolism)
Homeostasis – maintenance of optimal water potential of body fluids by regulating the water content, ion composition and pH of the body fluids; their role in the regulation of water content is described as osmoregulation

3. Vena
cava
Aorta l
Renal
vein
Renal
artery

4. The kidney is composed of three distinct regions
Kidney Section
Cortex
Pelvis
Medulla
The kidney is composed of three distinct regions

6. Draw diagrams to show the following structures:
Renal cortex
Medulla
Renal pyramid
Renal pelvis
Renal artery
Renal vein
Ureter
Bladder
Urethra

7. Kidney
dissection

8. Dissecting a Kidney: Safety
Scalpels are sharp!
Wear gloves and goggles at all times.
You are NOT a butcher – take care, small cuts only.
Label your kidney sections
Pins are sharp!
Do not dispose of kidney down the sinks, use the bin!
Wash desk tops down with disinfectant when you have finished.

10. The Kidney Tubule; Nephron
glomerulus
afferent
arteriole
efferent
arteriole
Bowman’s
(renal) capsule
distal
convoluted
tubule
proximal convoluted
tubule
branch from
renal artery
branch to
renal vein
collecting
duct
loop of Henlé
vasa recta
There are approximately one million kidney tubules in each human kidney

11. The nephron This is the functional unit of the kidney
It consists of a cup-shaped Bowman’s capsule connected to a tube which is divided into 3 regions
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
The ends of a number of nephrons join to form a collecting duct, which transfers fluid to the pelvis

12. The nephron ctd
Arteriole blood enters each capsule through an afferent arteriole (arrives)
This branches to form a dense capillary network, the glomerulus
Blood leaves the capsule through an efferent arteriole (exits)
This branches to form a network of capillaries, the vasa recta, around the nephron

13. Afferent vessel Efferent vessel outer layer Bowman’s capsule
inner layer
cavity
containing the
glomerulus

14. kidney animation

15. The filter
The plasma in the glomerulus is separated from the filtrate in the Bowman’s capsule by 3 layers:
The endothelium of the capillaries consisting of a single layer of squamous cells with pores between them.
The inner wall of the Bowman’s capsule consists of podocytes; these cells have foot-like processes which surround the capillaries and gaps called filtration slits.
Between these is the basement membrane, which is found on the outside of the capillary endothelium and is the effective filter.

16. The basement membrane is composed of glycoprotein and collagen fibres, forming a mesh; only molecules with a molecular mass less than
can pass through.
The filtrate will contain inorganic ions; glucose; amino acids; urea and other toxic substances dissolved in water.
Blood cells and most plasma proteins are too large to pass through.

17. filtration Efferent vessel Afferent vessel Basement membrane
Bowman’s capsule
glomerulus
podocytes
filtration
Endothelial
cells with pores
Glomerular filtrate
Glomerular capillaries containing glomerular plasma

18. glomerulus
capillary
podocyte
Use hair clasp to demo

20. Ultrafiltration The driving force behind ultrafiltration is the
high pressure of the blood entering the glomerulus.
P is high because:
The renal arteries are wide and relatively close to the heart
The afferent arteriole is wider than the efferent arteriole, creating a bottleneck
The high hydrostatic pressure created forces fluid from the glomerular plasma into the capsule, forming glomerular filtrate which enters the cavity of the Bowman’s capsule.

21. • The plasma proteins remaining in the glomerulus cause the water potential to decrease.
The filtrate entering the Bowman’s capsule causes the water potential here to increase.
• y filtrate now > glomerular plasma
This sets up an osmotic gradient from the filtrate in the nephron into the glomerular capillaries, called back pressure
which opposes the blood (hydrostatic) pressure
and resists further filtration.

22. FILTRATE ULTRAFILTRATION blood in glomerulus capillary
capillary endothelium
basement membrane
Podocytes on inner wall of Bowman’s capsule
lumen of
Bowman’s capsule
FILTRATE
Bowman’s capsule endothelium

23. The Kidney Tubule (Nephron)
Each kidney tubule is responsible for urine formation and this involves TWO basic processes:
Ultrafiltration of blood
plasma in the glomerulus is filtered into the Bowman’s capsule, all substances below a certain size are filtered, both useful and toxic
Selective tubular reabsorption of useful substances from the filtered materials
occurs as the filtrate passes along the nephron. The fluid is only called urine when it leaves the collecting ducts

24. Selective Reabsorption
As filtrate moves through the proximal convoluted tubule, 80% of the water is reabsorbed by osmosis into the adjacent blood capillaries of the vasa recta.
All glucose and amino acids are reabsorbed by active transport.
Small proteins, which may have been filtered are reabsorbed by pinocytosis.

25. Adaptations for Reabsorption
Cuboidal epithelial cells line the proximal convoluted tubule.
The surface in contact with the filtrate has many microvilli, and the surface next to the capillaries has many infoldings of the cell membrane (basal invaginations).
These adaptations increase the surface area for reabsorption.
These cells have many mitochondria that supply ATP for active transport.

26. The movement of solutes out of the proximal convoluted tubule by AT & pinocytosis lowers the solute potential in the cuboidal epithelium and blood capillaries;
This sets up an osmotic gradient between the proximal convoluted tubule and the blood capillaries causing water to move into the capillaries by osmosis.
This is responsible for the bulk of water reabsorbed in the kidney.

27. interstitial fluid
lumen
epithelial
cells
microvilli
intercellular
spaces
many
mitochondria

28. Microvilli
increase SA
Mitochondria:
Resp
Energy AT
Cell membrane infolding

29. urea water glucose sodium urea water sodium filtrate flow reabsorption
Microvilli
increase SA
reabsorption
 none
 some
 all
Not filtered
Intrinsic
carrier protein
for AT
 some
Mitochondria:
Resp
Energy AT
Blood flow

30. Distal
the ionic composition and pH of the blood are adjusted.
other toxic substances such as creatine, a waste product of metabolism, are secreted into the filtrate from the blood
facultative reabsorption of water, under the influence of the hormone ADH.

31. The Loop Of Henle
This is found deep in the medulla. Water and ions are moved between the filtrate in the loop and tissues in the medulla.
This causes the tissues deeper in the medulla to be more concentrated with ions, i.e. the solute potential becomes increasingly negative through the medulla.
Creates a salt gradient, and thereby increasingly negative solute potential,in the medulla tissue of the kidney.

32. This salt gradient is important in the reabsorption of water.
The Loop Of Henle
This salt gradient is important in the reabsorption of water.
This means there is a potential for osmotic extraction from the filtrate in the descending limb of the Loop of Henle, distal convoluted tubule and collecting duct.
It results in urine which is hypertonic to the blood.

33. Increasing concentration
The purpose of the
Loop of Henlé is to create a salt gradient (increasing concentration of salt) within the tissue
of the medulla
Increasing concentration
of salt
The water potential of the
descending limb is greater than the medulla therefore water is lost from the loop by osmosis allowing the production of concentrated urine
Water is not gained into or lost from the ascending limb as it is impermeable to water

34. Ultrafiltration of the blood takes place at the glomerulus
The Kidney
Tubule;
Nephron
Ultrafiltration of the blood
takes place at the glomerulus
Water reabsorption occurs from the distal convoluted tubule and collecting duct, allowing for the production of a concentrated urine
The glomerular filtrate flows into the proximal convoluted tubule where useful substances are reabsorbed back into the blood
The resulting fluid flows into the loop of Henlé where a salt gradient is created deep in the medulla
The walls of the distal tubules and collecting ducts are variably permeable to water, depending upon the presence or absence of antidiuretic hormone (ADH)

35. osmoregulation
Osmoreceptors in the hypothalamus are sensitive to the solute potential of the blood
Cells in the hypothalamus produce anti-diuretic hormone (ADH)
ADH is secreted into, stored and released from the posterior pituitary gland into the bloodstream

37. A rise in blood concentration (water potential more negative) is detected by the osmoreceptors,
Which send impulses to the posterior lobe of the pituitary gland
Resulting in release of ADH into the blood.

38. The water passes back into the blood capillaries of the vasa recta
ADH increases the permeability of the distal convoluted tubule and collecting ducts to water
When the walls are more permeable, more water is re-absorbed by osmosis, from
the filtrate in the distal convoluted tubule
the filtrate in the collecting duct
The water passes back into the blood capillaries of the vasa recta
A reduced volume of hypertonic urine is discharged.

39. blood solute potential
Thirst centre
cerebrum
blood solute potential
e.g. due to exercise,
little water intake,
high salt intake
More ADH
produced in the hypothalamus
and released from pituitary gland

40. Less water is reabsorbed producing large volumes of dilute urine
Less/no ADH
Produced or
released
blood solute potential
e.g. large water intake
Without ADH the walls of the distal convoluted tubules and collecting ducts remain relatively impermeable to water.
Less water is reabsorbed producing large volumes of dilute urine

41. ADH and negative feedback
No ADH produced
Less water reabsorbed
Large volumes dilute urine
increased
blood solute
potential
decreases
blood solute
potential
normal level
blood solute
normal level
blood solute
More ADH produced
More water reabsorbed
small volumes concentrated urine
increases
blood solute
potential
decreased
blood solute
potential
e.g. during exercise

42. Read page 321
Answer Q 6-10 page 325
Question booklet and answers

45. in excretion and osmoregulation
essay
describe and explain
the function of
the mammalian kidney
in excretion and osmoregulation