Excretory System

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

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

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

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

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

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

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

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

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

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)

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)

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)

Nephrostome Metanephridia Nephridio- pore Collecting tubule Bladder Capillary network Coelom

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

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

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

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

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

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 http://hypertextbook.com/facts/2001/DanielShaw.shtml

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

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

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

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

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

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

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

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

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

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

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.

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

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

The Urinary System Overview

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

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)

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)

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

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

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

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

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