Presentation 15: Excretory system

Question 1

Function of excretory system

Answer 1

• Excretes N2 (nitrogen) waste from metabolism of proteins and excess water/salts
• Maintains proper internal environment

Question 2

Describe the invertebrate excretory system

Answer 2

Have metanphridia (excretory structure)
- numerous (1 per segment) nephritic tubules (renal tubules) that opened directly into the coelom via nephrostomes and empties out of the body through nephridiopore
- recovery of products through filtration through a knot of capilaries called glomerulus

Question 3

Vertebrate Excretory system

Answer 3

Evolved glomerulus and nephritic tubules into renal corpuscle composed of outer layer called renal capsule (aka Bowman’s capsule) and inner glomerulus.
together the renal corpsucle and its associated tubes are called the nephron

Question 4

Nephron

Answer 4

Main part of kidneys that function as excretory
(Renal corpuscle and associated tubules)
Found in cortex of kidneys

Question 5

What are the tubes associated with the renal corpuscle?

Answer 5

Proximal tubule
Distal Tubule
Collecting duct
Loop of Henle (only in birds + mammals)

Question 6

What are the different ways to categories the development of the kidney?

Answer 6

Ontogenetic (aka development of individuals)
- Pronephros
- Mesonephros
- Metanephros
Phylogenetic (evolution between species)
- Holonephros
- Opistonephros
- Metanephros

Question 7

Holonephros

Answer 7

Hypothetical ancestral condition
- ancestrally segmented anteriorly and a single unit posteriorly
- anteriorly neohrostomes
- posteriorly nephrogenic chord (not totally combined but not totally seperate)
- drains via the archinephritic duct

Question 8

Opistonephros

Answer 8

MESONEPHROS
Nephrostomes form but are absent in adult (functional in nonamniotes)

Question 9

Pronephros

Answer 9

Head kidney - present in larval and adult fishes + larval amphibians
- 1-12 pairs of nephrostomes
- functional in hagfishes but nephrostomes fuse forming a glomus
- empties through pronephric duct

Question 10

Glomus

Answer 10

fused nephrostomes in hagfish (functioning pronephros)

Question 11

Mesenephros

Answer 11

develops in all vertebrates but absent in adult amniotes/mammals (functional in nonamniotes e.g. amphibians, frogs, salamanders, reptiles, birds)
- drained via mesenephric duct

Question 12

Metanephros

Answer 12

Posterior part, never segmented
- drained by ureter which first appears as an outgrowth of the mesenephric duct called the ureteric bud near the entrance of cloaca
- branches off within kidney (collecting tubules)

Question 13

Internal gross anatomy of kidney

Answer 13

In birds + mammals, kidney is organized into distinct renal cortex (where nephrons/corpsucles reside) and renal medulla (where associated tubules reside)
- renal medulla extends off minor calyx which branches off major calyx
- major calyxes come together to form renal pelvis which connects to the ureter (drains kidney)
- kidney is irrigated by renal vein and artery
- duct of metaneophros or ureter branches off w/in kidney = collecting tubules
- renal papillae collect into calyx and are between branches of the renal pelvis

Question 14

Nephritic tubules

Answer 14

Proximal and distal convoluted tubule that are connected by loop of henle in birds/mammals and empty into a collecting duct
- Proximal convoluted tube (reabsorbs sugars, amino acids, vitamins and salts)
- Distal convoluted tube (reabsorbs potassium, calcium, sodium, and chloride ions)
- both tubes may return water to blood

loop of henle = water reabsorption

Question 15

Proximal convoluted tubule

Answer 15

part of nephritic tubule closest to renal corpuscle
- low cuboidal columnar cells w/ microvilli
-reabsorbs sugars, amino acids, vitamins and salts
- returns water to blood

Question 16

Distal convoluted tubule

Answer 16

part of nephritic tubule closest to collecting duct
- cuboidal cells
- reabsorbs potassium, calcium, sodium, and chloride ions
- returns water to blood

Question 17

Loop of henle

Answer 17

independantly evolved in both mammals and birds
- intermediate loop
- primarily reabsorbs water
- thin = descendent - reabsorbs water
- thick = ascendent - reabsorbs 1/4 Na, Cl, + K that is eliminated w/ water

Question 18

Fish Body fluids balance

Answer 18

Marine fish = hypotonic
- small renal corpuscle to conserve water
- large nephritic tubules to reabsorb water
- gills excrete salt that is uptaken with saltwater and also urea (nitrogen waste)

Freshwater fish = hypertonic
- large renal corpuscle to excrete
- short nephritic tubules to not uptake too much water

Question 19

How is Nitrogen and other waste eliminated in different vertebrates?

Answer 19

Marine vertebrates (fish) = N via urea via gills

Freshwater vertebrates (fish amphibians) = N in ammonia excreted through gills

Adult amphibians = N via Urea excreted via kidney

Sharks = N via urea excreted through kidneys, gills, + rectal gland

Reptiles/Birds = N via Uric acid (insoluble in water), salt excreted in urine

Mammals = N via Urea (99% water is reabsorbed)

Question 20

What are the different parts of the Renal Corpuscle?

Answer 20

BOWMAN’s CAPSULE:
- Podocytes = cells that wrap around cappilaries of the glomerulus (aka visceral layer)
- Parietal layer = outer layer

Poles:
- Urinary pole where waste flows down to go to nephritic tubules (aka proximal convoluted tubule)
- Vascular pole (where Renal arteries and veins are (afferent and efferent arterioles)
- Macula densa = key sensory and regulatory functions in the maintenance of body fluid, electrolyte homeostasis, + bloodpressure

Question 21

Urinary bladder diversity

Answer 21

Agnatha: Absent

Fishes:
- firms enlargement of nephritic duct near caudal ends of mesonephric duct
- doesn’t function in urine storage

Tetrapods:
- develops as an evagination from ventral side of the cloaca
- absent in crocodiles, snakes, some lizards, and most birds
- storage area for urine
- resivoir of water during times of dehydration
- bladder empties into the cloaca

Therian mammals: separate opening = urethra
- wall of bladder = longitudinal and circular smooth muscle