1. Topic 11.3 The Kidney & Osmoregulation

2. Excretory System
Function is to rid the body of toxic waste through excretion
Excretion: the removal of waste products of metabolic processes in the body

3. Types of Regulation
Osmoconformers: maintain solute concentrations in their body tissues that are isotonic to the surrounding environment.
Saltwater fish (sharks etc.)
Osmoregulators: have adaptations to live in aquatic environments that are not isotonic to their body tissues.
Freshwater fish

4. Types of regulation Cont.
Malpighian Tubules: osmoregulation by insects
Absorb salt, water and waste
Mammals: osmoregulation by mammals using the kidneys
use nephrons to regulate concentration of substances

5. The Human Excretory System
Consists of the following parts
Kidneys
Ureters
Urinary Bladder
Urethra
Kidneys carry out
Both excretion and
Osmoregulation
The filtrate eventually
Becomes urine

7. Parts of the Kidney Outside is called the renal cortex
Middle is called the renal medulla
Inner funnel shaped section is called the renal pelvis
Renal artery brings blood into the kidneys
Renal vein takes blood away from the kidneys

9. The Nephron The functional unit of the kidney Ultrafiltration
Selective reabsorption
Secretion
excretion

10. Functions of the Nephron
Location
Process
Ultrafiltration
Glomerulus
Filters small molecules through fenestrations (pores) in the capillaries from the blood into the Bowman’s capsule (urea, salts, glucose, amino acids). Large proteins & blood cells are too large to fit in pores so they stay in the blood capillaries
Selective reabsorption
Proximal convoluted tubule
Glucose, amino acids & salts are reabsorbed back into blood capillaries. Actively pumped out of the proximal convoluted tubule & water follow possibly by osmosis
Secretion
Distal convoluted tubule
Toxins & metabolites of drugs are pumped into the tubule to be excreted from the body
Excretion
Collecting duct
Urea, some salts, water, ammonia & toxins are excreted from nephron & ultimately from the body as components of urine.

11. The Glomerulus Helps with ultrafiltration 3 parts
Fenestration: pores between cells in the wall of capillaries that allow fluid to escape, but not blood cells
The basement membrane: covers and supports the wall of capillaries. Prevents plasma proteins from being filtered out.
Podocytes: form inner wall of Bowman’s capsule (foot like projections) prevents small molecules from being filtered out of the blood

12. Glomerulus

13. The Proximal Convoluted Tubule
Selectively reabsorbs useful substances by active transport
Most filtrate from glomerulus is reabsorbed
Most happens in the PCT
By the end of the PCT all glucose and amino acids & 80% of the water, sodium and other mineral ions have been reabsorbed

14. The Loop of Henle Maintains hypertonic conditions in the renal medulla
Sodium ions are pumped out of the filtrate to the fluid between the cells in the medulla and the interstitial fluid
The Ascending limb is permeable to salts, but impermeable to water; water is retained
The descending limb is permeable to water but impermeable to sodium ions
Longer loops of Henle are found in animals that need to conserve more water
Then moves to DCT Distal convoluted tubule

15. Loop of Henle

16. Role of ADH ADH = Antidiuretic Hormone
Filtrate in the DCT concentration is lower than that of normal body fluids (hypertonic)
If the solute concentration of blood is too low litter water is reabsorbed
If the solute concentration of the blood is too high they hypothalamus causes the pituitary to secrete ADH.
ADH causes the walls of the DCT and collecting duct to become more permeable to water

17. Protein, Glucose & Urea Filtration
Molecule
Present in Blood Plasma
Present in Glomerular Filtrate
Present in Urine
Proteins
Yes
No (Too large to undergo ultrafiltration) No
Glucose
No (selectively reabsorbed since it is vital for cellular respiration
Urea
Yes (excreted since it is a toxin)

18. Glucose in Urine & Diabetes
Presence of glucose in the urine is the main identifying feature of diabetes
High level of glucose present in glomerular filtrate and enters the PCT

19. Nitrogenous Waste
Organisms have evolved to excrete ammonia, urea or uric acid
Directly related to the environment in which they live
Freshwater organisms can easily secrete ammonia into their environment
Terrestrial animals need to convert ammonia to urea or uric acid

20. Renal Arteries Vs. Renal Veins
Composition of Blood in the Renal Artery & Renal Vein
Renal Artery
Renal Vein
Oxygen levels
High
Low (used for cellular respiration by cells in the kidney)
Carbon Dioxide levels
Low
High (given off by kidney cells during cellular respiration
Urea (nitrogenous wastes)
Low (removed during ultrafiltration and remains in the filtrate for excretion from the body)
Glucose
Slightly high
Slightly low (most is actively reabsorbed in the proximal convoluted tubule – some is used by the kidney for cellular respiration

21. Stuff to Know Afferent: Going towards, moving into
Efferent: Going away from, moving out