1. Excretory System

2. Purpose: Maintain homeostasis by regulating water balance and by removing harmful substances (nitrogenous waste from protein digestion)

3. Nitrogenous Waste Removal
Aquatic: excrete NH3 – ammonia – highly toxic but very soluble – FISH
Land: Urea – less toxic but less water soluble – requires more water for removal

4. 3. Uric Acid: insoluble in water – forms a solid and requires little water for removal – less likely to seep into tissues since its insoluble – forms a pastelike substance which requires less water for excretion – good for BIRDS and REPTILES
– keeps waste from poisoning eggs during development and keeps birds from having extra water waste which would weigh them down for flying

5. 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
NH3
NH2 O C N H HN

6. Marine Fish: Hypotonic tissues: more solute outside of the body
Osmoregulation: absorption and secretion of water and solutes to maintain proper water balance of an organism and its surroundings
Marine Fish:
Hypotonic tissues: more solute outside of the body
Flow of water out of the fish  dehydrate
Responses:
- constant drinking
- infrequent urination
- excretion of salt from gills

7. Gain of water and
salt ions from food
and by drinking
seawater
Osmotic water loss
through gills and other parts
of body surface
Excretion of
salt ions
from gills
Excretion of salt ions
and small amounts
of water in scanty
urine from kidneys

8. 2. Fresh Water Fish:
- Hypertonic tissues: more solute in the body
- flow of water into the tissues
Responses:
- little drinking
- frequent urination
- absorption of salt by gills

9. Uptake of
water and some
ions in food
Osmotic water gain
through gills and other parts
of body surface
salt ions
by gills
Excretion of
large amounts of
water in dilute
urine from kidneys

10. Excretory Mechanisms Contractile Vacuole: Protists
- vacuoles that accumulate water and then merge with the plasma membrane and release the water outside of the cell
Video #2

12. 2. Flame Cells: Platyhelminthes (Planaria)
Clusters of cilia moving body fluids through a system of tubes
Wastes in tube exit out of the body by pores (nephridiopores)

13. Nucleus
of cap cell
Cilia
Interstitial fluid
filters through
membrane where
cap cell and tubule
cell interdigitate
(interlock)
Tubule cell
Flame
bulb
Nephridiopore
in body wall
Tubule
Protonephridia
(tubules)

14. 3. Nephridia (metanephridia): Annelids
- pairs of tube systems in each segment
Takes in interstitial fluid through the nephrostome (ciliated intake)
Selective secretion of materials as fluid passes through collecting tube
Retained materials pass into coelom and into capillaries for circulation
Concentrated wastes exit through the excretory pore (nephridiopore)

15. Nephrostome
Metanephridia
Nephridio-
pore
Collecting
tubule
Bladder
Capillary
network
Coelom

16. 4. Malpighian Tubules: Insects
System of tubes attached to the mid-gut of the digestive system
Collect materials from the hemolymph and deposit them into the digestive system – open circulatory system
Digestive system absorbs materials while wastes are excreted

17. Digestive tract
Midgut
(stomach)
Malpighian
tubules
Rectum
Intestine
Hindgut
Salt, water, and
nitrogenous
wastes
Feces and urine
Anus
tubule
Reabsorption of H2O,
ions, and valuable
organic molecules
HEMOLYMPH

18. 5. Kidney: absorbs water and nutrients from the blood and concentrates urea for excretion
Kidney Structure:
Cortex: lowest osmolarity in interstitial fluid (allows for the absorption of materials) – outermost layer of kidney
Medulla: highest osmolarity – allows for the retention of water – inner portion of kidney
Renal Pelvis: collects urea and wastes
Contains NEPHRONS: tube for absorption and secretion – functional unit of the kidney

19. Section of kidney from a rat
(b) Kidney structure
Ureter
Section of kidney from a rat
Renal
medulla
cortex
pelvis
Figure 44.13b

20. Juxta- Cortical medullary nephron Renal cortex 20 µm medulla To renal
Collecting
duct To
renal
pelvis
Renal
cortex
medulla
20 µm
Afferent
arteriole
from renal
artery
Glomerulus
Bowman’s capsule
Proximal tubule
Peritubular capillaries
SEM
Efferent
arteriole from
glomerulus
Branch of
renal vein
Descending
limb
Ascending
Loop of
Henle
Distal
tubule
(c) Nephron
Vasa recta
(d) Filtrate and
blood flow

21. Kidney Filtration Facts
Each Minute the pair of kidneys
Filters 1200 cc (mL) of blood
Which makes 125 cc of filtrate
Of which 124 cc are reclaimed
Making 1 cc of urine
“The majority of sources that I found reported that the adult bladder could contain about 600 to 800 cm3 (ml). However, they also noted that the Micturition point is between 150 and 300 cm3 (ml).” - Daniel Shaw – 2001

22. Structure of Nephron/Path of Filtrate
Cortex:
Bowman’s Capsule
Proximal Tubule
Medulla
Descending Loop of Henle
Ascending Loop of Henle
Cortex
Distal Tubule
Collecting Duct

23. Juxta- Cortical medullary nephron Renal cortex 20 µm medulla To renal
Collecting
duct To
renal
pelvis
Renal
cortex
medulla
20 µm
Afferent
arteriole
from renal
artery
Glomerulus
Bowman’s capsule
Proximal tubule
Peritubular capillaries
SEM
Efferent
arteriole from
glomerulus
Branch of
renal vein
Descending
limb
Ascending
Loop of
Henle
Distal
tubule
(c) Nephron
Vasa recta
(d) Filtrate and
blood flow

24. Path of Blood Vessels Renal Artery
Bowman’s Capsule and Glomerulus (cluster of capillaries)
Proximal and Distal Tubules
Ascending Loop of Henle
Descending Loop of Henle
Renal Vein

25. Juxta- Cortical medullary nephron Renal cortex 20 µm medulla To renal
Collecting
duct To
renal
pelvis
Renal
cortex
medulla
20 µm
Afferent
arteriole
from renal
artery
Glomerulus
Bowman’s capsule
Proximal tubule
Peritubular capillaries
SEM
Efferent
arteriole from
glomerulus
Branch of
renal vein
Descending
limb
Ascending
Loop of
Henle
Distal
tubule
(c) Nephron
Vasa recta
(d) Filtrate and
blood flow

26. Counter Current Flow Cortex: Bowman’s Capsule Proximal Tubule
Medulla
Descending Loop of Henle
Ascending Loop of Henle
Cortex
Distal Tubule
Collecting Duct
Renal Artery
Bowman’s Capsule and Glomerulus (cluster of capillaries)
Proximal and Distal Tubules
Ascending Loop of Henle
Descending Loop of Henle
Renal Vein

27. NOTE: Around the Loop of Henle: Blood flows in the opposite direction of the filtrate inside the loop

28. Excretion Process Bowman’s Capsule:
End of the nephron surrounding a cluster of capillaries (glomerulus)
Afferent arteriole enters the Bowman’s capsule to form the glomerulus and leaves as the efferent arteriole
Bowman’s capsule absorbs water, sugar, salts and wastes from the glomerulus due to the pressure forcing the materials out
Larger components of blood (RBC’s, platelets, large proteins) remain in the blood vessel

29. 2. Proximal Convoluted Tubule (PCT):
- Secretion and absorption of materials by the kidney
Kidney secretes H+ ions, ammonia into the PCT – maintains pH
- the materials become part of the filtrate (solution inside of the nephron)
Capillaries around the PCT reclaim salt, bicarbonate, sugars and water

30. 3. Descending Loop of Henle
Permeable to water but not to salt
Site of water reclamation
Water is absorbed into the capillaries
Filtrate becomes more concentrated as the salt remains in the filtrate

31. 4. Ascending Loop of Henle
- permeable to salt but not to water
- salt is reclaimed by the capillaries and filtrate becomes less concentrated

32. IMPORTANCE: Counter current flow of capillaries to filtrate path in the nephron
First, the blood in the capillary picks up salt by active transport as it travels past the ascending loop
This raises the osmolarity of the blood allowing for the reabsorption of water as it flows up the descending loop.

33. 5. Distal Convoluted Tubule
- Regulates the K+ and the NaCl levels

34. 6. Collecting Duct
- Allows for the reclamation of water and salt to maintain balance in kidney
carries the filtrate to the renal pelvis which connects to the ureter which empties into the bladder
The bladder empties through the urethra

35. The Urinary System Overview

36. Osmolarity Control of Urine Content:
Antidiuretic Hormone (ADH)
- produced in the hypothalamus
- stored and released in the pituitary gland

37. Loss of water (sweating, lack of intake) increases the blood osmolarity
Chemosensors in hypothalamus sense the high levels and secrete ADH
ADH travels to the distal tube and the collecting duct making them MORE permeable to water increasing the absorption of water and concentrating the urine (pee is darker)

38. Excess water in the blood (from drinking 3 nalgenes of water a day) causes little ADH to be released so the uptake of water is limited causing the urine to be dilute and increased urination (diuresis)
ADH counters diuresis
Substances that increase diuresis are called diuretics (caffeine and alcohol)

39. hypothalamus detect an increase in the osmolarity of the blood
Osmoreceptors
in hypothalamus
Drinking reduces
blood osmolarity
to set point
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
Homeostasis:
Blood osmolarity
Hypothalamus
ADH
Pituitary
gland
Increased
permeability
Thirst
Collecting duct
Distal
tubule

40. 2. Renin-Angiotensin-Aldosterone System (RAAS): response to a drop in blood pressure or volume
- Juxtaglomerular Apparatus responds by releasing Renin
- Renin causes the blood protein Angiotensin to be converted into Angiotensin II which stimulates the constriction of blood arterioles

41. Blood vessel constriction narrows the diameter and increases pressure
WHY? Keep blood pumping to brain
Angiotensin also stimulates the secretion of Aldosterone from the adrenal gland (located on top of the kidney)
Aldosterone increases the absorption of NaCl and water which raises the blood volume and pressure

42. apparatus (JGA) responds to low blood volume or
Increased Na+
and H2O reab-
sorption in
distal tubules
Homeostasis:
Blood pressure,
volume
STIMULUS:
The juxtaglomerular
apparatus (JGA) responds
to low blood volume or
blood pressure (such as due
to dehydration or loss of
blood)
Aldosterone
Adrenal gland
Angiotensin II
Angiotensinogen
Renin
production
Arteriole
constriction
Distal
tubule
JGA

43. RAAS is countered by the secretion of Atrial Natriuretic Factor from the atrial wall – this is a response to blood pressure that is too high (pressure on the atrial wall is the signal)
- ANF blocks the production of renin