1. Osmoregulation and Excretion
The Kidney
Osmoregulation and Excretion
Crash course video link below:

2. IB Learning Objectives
Define excretion.

4. Overview: A Balancing Act
Physiological systems of animals operate in a fluid environment
Relative concentrations of water and solutes must be maintained within fairly narrow limits

5. Excretion definition –
Chemical reactions of metabolism produce byproducts (waste).
These byproduct can be toxic if the accumulate
Excretion is the removal from the body the waste products of metabolism.

6. Osmoregulation, Homeostasis and Excretion
Excretion plays an important role in maintaining homeostasis.
Associated with both homeostasis and excretion is the process of osmoregulation.

7. IB Learning Objective
Define osmoregulation

8. Osmoregulation and Excretion
Osmoregulation regulates solute concentrations and balances the gain and loss of water
Excretion gets rid of metabolic wastes

9. Osmosis
Cells require a balance between osmotic gain and loss of water

10. Water balance in a kangaroo rat (2 mL/day) Water balance in a human
LE 44-5
Water
balance in a
kangaroo rat
(2 mL/day)
Water
balance in
a human
(2,500 mL/day)
Ingested
in food
(750 mL)
Ingested
in food (0.2 mL)
Ingested
in liquid
(1,500 mL)
Water
gain
Derived from
metabolism (1.8 mL)
Derived from
metabolism (250 mL)
Feces (0.09 mL)
Feces (100 mL)
Urine
(1,500 mL)
Urine
(0.45 mL)
Water
loss
Evaporation (1.46 mL)
Evaporation (900 mL)

11. 4 3 (L/100 kg body mass) Water lost per day 2 1 Control group
LE 44-6 4 3
(L/100 kg body mass)
Water lost per day 2 1
Control group
(Unclipped fur)
Experimental group
(Clipped fur)

12. An animal’s nitrogenous wastes reflect its phylogeny and habitat
The type and quantity of an animal’s waste products may greatly affect its water balance
Among the most important wastes are nitrogenous breakdown products of proteins and nucleic acids

13. Forms of Nitrogenous Wastes
Different animals excrete nitrogenous wastes in different forms: ammonia, urea, or uric acid

14. LE 44-8 Proteins Nucleic acids Amino acids Nitrogenous bases —NH2
Amino groups
Most aquatic animals, including most bony fishes
Mammals, most amphibians, sharks, some bony fishes
Many reptiles (including birds), insects, land snails
Ammonia
Urea
Uric acid

15. Urea
The liver of mammals and most adult amphibians converts ammonia to less toxic urea
The circulatory system carries urea to the kidneys, where it is excreted

16. IB Learning Objective Draw and label a diagram of the kidney.
Include the cortex, medulla, pelvis, ureter and renal blood vessels.

19. Excretory Processes
Most excretory systems produce urine by refining a filtrate derived from body fluids
Key functions of most excretory systems:
Filtration: pressure-filtering of body fluids
Reabsorption: reclaiming valuable solutes
Secretion: adding toxins and other solutes from the body fluids to the filtrate
Excretion: removing the filtrate from the system

20. LE 44-9 Capillary Filtration Excretory tubule Reabsorption Secretion
Filtrate
Reabsorption
Secretion
Urine
Excretion

21. The Kidney
The kidneys regulate the amount of water, salts and other substances in the blood.
The kidneys are fist-sized, bean shaped structures that remove nitrogenous wastes (urine) and excess salts from the blood
Because the kidney regulates both salt and water concentration in the blood it is the central organ that controls osmoregulation.

22. The Kidney

23. The urinary system: The pathway of Urine to the outside the body.
The ureters are tubes that carry urine from the pelvis of the kidneys to the urinary bladder.
The urinary bladder temporarily stores urine until it is released from the body.
The urethra is the tube that carries urine from the urinary bladder to the outside of the body.
The outer end of the urethra is controlled by a circular muscle called a sphincter.
These parts work together and are part of the urinary system.

24. Blood vessels of the mammalian kidney
Each kidney is supplied with blood by a renal artery and drained by a renal vein
Animation: Nephron Introduction

25. The Kidney

26. The kidney structure Each kidney is composed of three sections:
The cortex is where the blood is filtered.
The medulla contains the collecting ducts which carry filtrate (filtered substances) to the pelvis.
The pelvis is a hollow cavity where urine accumulates and drains into the ureter.

27. The Kidneys Cortex Renal artery Medulla Renal vein Ureter
To the bladder

28. The medulla and cortex
The outer cortex and inner medulla are made up of a million or more tiny tubules called nephrons.
Part of a nephron is in the medulla the other part is in the cortex.
Nephrons is a thin walled tubules about (3 cm) long.

29. LE 44-13 Posterior vena cava Renal artery and vein Kidney Renal
medulla
Aorta
Renal
cortex
Ureter
Renal
pelvis
Urinary bladder
Urethra
Excretory organs and
major associated blood
vessels
Ureter
Kidney structure
Section of kidney from a rat
Juxta-
medullary
nephron
Cortical
nephron
Afferent
arteriole
from renal
artery
Glomerulus
Bowman’s capsule
Proximal tubule
Renal
cortex
Peritubular capillaries
Collecting
duct
SEM
20 µm
Efferent
arteriole from
glomerulus
Renal
medulla
Distal
tubule To
renal
pelvis
Branch of
renal vein
Collecting
duct
Descending
limb
Loop of
Henle
Nephron
Ascending
limb
Vasa
recta
Filtrate and blood flow

30. The Kidneys Structure of the Kidneys Kidney Nephron
Kidneys are made up of nephrons. Blood enters the nephron, where impurities are filtered out and emptied into the collecting duct. The purified blood leaves the nephron through the renal vein.

32. IB Learning Objective
Annotate a diagram of a glomerulus and associated nephron to show the function of each part.

33. Parts of the Nephron Each nephron consists of the following parts:
1) glomerulus ;
2) Bowman’s capsule ;
3) proximal tubule ;
4) loop of Henle ;
5) distal (convoluted) tubule ;
6) collecting duct.

34. Capillaries Bowman’s capsule Glomerulus Collecting duct Vein Artery
Loop of Henle
Bowman’s capsule
Glomerulus
Capillaries
Collecting duct
To the ureter
Kidneys are made up of nephrons. Blood enters the nephron, where impurities are filtered out and emptied into the collecting duct. The purified blood leaves the nephron through the renal vein.

37. Functions of the parts of the Kidney
The glomerulus is a mass of thin-walled capillaries.
The Bowman’s capsule is a double-walled, cup-shaped structure.
The proximal tubule leads from the Bowman’s capsule to the Loop of Henle.
The loop of Henle is a long loop which extends into the medulla.
The distal tubule connects the loop of Henle to the collecting duct.

38. IB LEARNING OBJECTIVE
Explain the process of ultrafiltration, including blood pressure, fenestrated blood capillaries and basement membrane

39. Five Steps in the Formation of Urine
Ultrafiltration in the renal capsule
Selective reabsorption in the proximal convoluted tubules
Water conservation in the loop of henle (osmoregulation)
Blood pH and ion concentration regulation in the distal convoluted tubule (osmoregulation)
Water reabsorption in the collecting ducts. (osmoregulation)

41. Step 1: Ultrafiltration in the renul capsule.
Filtration occurs as blood pressure forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule
This process is called Ultrafiltration because it is powered by pressure of the blood.
The entire content of the blood is not forced out.
The basement membrane of the of the capsule does not allow blood cells and proteins to enter the filtrate.

43. IB Learning Objective
Explain the reabsorption of glucose, water and salts in the proximal convoluted tubule, including the roles of
microvilli,
osmosis
and active transport.

44. Step 2 : Selective reabsorption in the proximal convoluted tubules
The convoluted proximal tubules is the longest section of the nephron.
The walls are one cell thick and they are packed with mitochondria.
The cell membrane in contact with the filtrate is packed with microvilli to increase surface area for absorption.

45. Step 2 : Selective reabsorption in the proximal convoluted tubules (see figure 12.22 page 373)
The proximal convoluted tubules absorb filtrate through the following mechanisms:
Movement of water via osmosis
Active transport of glucose and amino acids across membranes
Movement of some minerals and ions via a combination of active transport, facilitated diffusion and some gas exchange of ions
Diffusion of urea
Movement of protein via pinocytosis (endocytosis)

46. Step 3 Water conservation in the loop of henle
Urea is excreted from the body in solution, thus water loss is inevitable
Water loss is minimized by having the solutes concentration in urine higher than the blood.
The role of the loop of Henle is to maintain a high concentration of solutes in the medulla of the kidney
The loop of henle has a descending and ascending limbs that parallels the blood supply.

48. LE 44-14 Proximal tubule Distal tubule NaCl Nutrients H2O HCO3– H2O K+
NH3 K+ H+
CORTEX
Descending limb
of loop of
Henle
Thick segment
of ascending
limb
Filtrate
H2O
Salts (NaCl and others)
HCO3– H+
Urea
Glucose; amino acids
Some drugs
NaCl
H2O
OUTER
MEDULLA
NaCl
Thin segment
of ascending
limb
Collecting
duct
Key
Urea
Active transport
Passive transport
NaCl
H2O
INNER
MEDULLA

49. IB LEARNING OBJECTIVE
Explain the roles of the loop of Henle, medulla, collecting duct and ADH (vasopressin) in maintaining the water balance of the blood.

51. Step 3 Water conservation in the loop of henle figure 12.23 page 374
The descending limb is permeable so salt diffuses into the loop of Henle and water diffuses out into the medulla tissue.
At the hairpin zone (base of the loop) water and salt diffuse into the medulla tissue.
In the ascending limb of the loop of Henle, salt diffuses from the permeable loop tubule into the interstitial fluid of the medulla, but water is retained

52. Step 4: Blood pH and ion concentration regulation in the distal convoluted tubule
The distal tubule cells are the same as in the proximal tubule (one cell thick, microvilli and lots of Mitochondria)
The role of the distal tubule cells is to adjust the composition of the blood, in particular pH.
Blood pH is initially buffered by blood proteins, but if it deviates from a pH of 7.4 the concentrations of Hydrogen ion (H+) and hydroxide (OH-) are adjusted
Blood pH does not vary outside the range of pH 7.35 to 7.45, but urine pH ranges from 4.5 to 8.2.

53. Step 5: Water reabsorption in the collecting ducts.
The collecting ducts are where the water content is regulated.
When the water content of the blood is low the antidiuretic hormone (ADH) is secreted from the posterior pituitary gland.
When the water is the blood is high, NO ADH is released.

55. Step 5: Water reabsorption in the collecting ducts.
The permeability of the walls of the collecting ducts are variable.
If ADH is present the walls of the collecting tubules become fully permeable.
This allows water to be withdrawn from the filtrate of the tubule in the medulla.
The water will be taken up and redistributed throughout the body.
ADH is remove from the body by the kidney
When no ADH is present the walls of the collecting duct become less permeable.

58. Kidney Animations/ tutorials
Hormonal Control Animation

59. hypothalamus detect an increase in the osmolarity
LE 44-16a
Osmoreceptors
in hypothalamus
Thirst
Hypothalamus
Drinking reduces
blood osmolarity
to set point
ADH
Increased
permeability
Pituitary
gland
Distal
tubule
H2O reab-
sorption helps
prevent further
osmolarity
increase
STIMULUS
The release of ADH is
triggered when osmo-
receptor cells in the
hypothalamus detect an
increase in the osmolarity
of the blood
Collecting duct
Homeostasis:
Blood osmolarity

60. IB Learning Objective
Explain the differences in the concentration of proteins, glucose and urea between blood plasma, glomerular filtrate and urine.

61. Differences in the composition of blood plasma, glomerular filtrate and urine
The composition excrete from urine is variable.
Greatly influenced by six factors
Diet (salt intake, protein consumed)
Physical Activity
Water intake
Amount of sweating
Environmental condition
State of health (i.e. Diabetics)

62. Differences in the composition of blood plasma, glomerular filtrate and urine
The composition of blood is constant
Constancy is due to the efficiency of our homeostatic mechanisms

63. Differences in the composition of blood plasma, glomerular filtrate and urine
The composition of glomerular filtrate (ultrafiltration of the glomerus) is constant
Constancy is due to the ultrafiltration, the pressure of the blood, and the size of blood proteins that are too large to filter.

65. IB Learning Objectives
Explain the presence of glucose in the urine of untreated diabetic patients.

69. The composition of the urine of a diabetic patient
The disease known as diabetes – blood glucose levels are erratic and frequently above normal.
A consequence to this elevated blood glucose level is the failure of the kidney tubules to reabsorb all the glucose forced out of the blood.
Thus the urine of a diabetic generally contains a lot of glucose.
Raise glucose level in the urine is a symptom of a patient being a diabetic.

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