Osmoregulation Chapter 44

Osmoregulation Balance of water & solute concentration Intracellular & extracellular Ions (solutes) Na+1, Cl-1

Osmolarity Hyperosmotic Hypoosmotic Isoosmotic Normal saline (0.9%) 5% dextrose

Selectively permeable membrane Solutes Water Hyperosmotic side: • Higher solute concentration • Lower free H2O concentration Hypoosmotic side: • Lower solute concentration • Higher free H2O concentration Figure 44.2 Solute concentration and osmosis Net water flow

Osmoregulation Osmocomfomers Body fluids have same concentration as environment Ocean invertebrates Osmoregulators Constant blood osmolarity Vertebrates

Osmoregulation

(a) Hydrated tardigrade (b) Dehydrated tardigrade 50 µm Figure 44.5 Anhydrobiosis (a) Hydrated tardigrade (b) Dehydrated tardigrade

Nitrogenous wastes Proteins, DNA & RNA contain nitrogen Break downs-waste (NH2) Aquatic animals NH3 Mammals, amphibians Urea Birds, reptiles, insects Uric acid

Nitrogenous wastes

Urea Uric acid

Most aquatic animals, including most bony fishes Mammals, most Nitrogen wastes 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

Excretory process Excretory systems Regulate solute concentrations Produce urine Refine filtrate from body fluids

Excretory process Filtration Blood (body fluids) is filtered Forms filtrate (urine) Reabsorption Ions & nutrients are recovered Returned to body from filtrate

Excretory process Secretion Wastes/water from capillaries to filtrate (urine) Excretion Release filtrate (urine) from body Release nitrogenous metabolites

Filtration Capillary Excretory tubule Reabsorption Secretion Excretion Filtrate Excretory tubule Reabsorption Secretion Urine Excretion

Excretory Organs Nephron Types Kidney Structure Figure 44.12a Renal cortex Cortical nephron Juxtamedullary nephron Renal medulla Posterior vena cava Renal artery Renal artery and vein Kidney Renal vein Aorta Renal cortex Ureter Figure 44.12a Exploring the mammalian excretory system (part 1) Ureter Urinary bladder Renal medulla Urethra Renal pelvis

Anatomy Kidney Ureter Bladder Urethra Renal artery/vein Blood supply of kidney

Anatomy Renal cortex Outside of kidney Renal medulla Inside of kidney (hypertonic) Renal pelvis Funnel shaped Ureter meets kidney

Kidney

Anatomy Nephron: Functioning unit of kidney 1 million in each kidney Glomerulus Bowman’s capsule Proximal (convoluted) tubule Loop of henle Distal (convoluted) tubule

Nephron

Kidney

Kidney

Pathway

Pathway through kidney Blood forced into glomerulus Bed of capillaries Blood cells & proteins are too large Plasma goes through with minerals & water Filtrate Enters Bowman’s capsule Proximal tubule Located in renal cortex

Pathway through kidney Enters loop of Henle In the loop goes deep in the renal medulla Fluid returns Distal tubule Drains into collecting duct Goes into renal pelvis (urine) Ureter

Pathway through kidney

Juxtamedullary Cortical nephron nephron Renal cortex Collecting duct To renal pelvis (c) Nephron types

Nephron

Pathway through kidney Capillaries surround the loop Reabsorb water & ions

10 µm Afferent arteriole from renal artery Glomerulus Bowman’s capsule Nephron Afferent arteriole from renal artery Glomerulus 10 µm Bowman’s capsule SEM Proximal tubule Peritubular capillaries Efferent arteriole from glomerulus Distal tubule Branch of renal vein Collecting duct Descending limb Loop of Henle Ascending limb Vasa recta (d) Filtrate and blood flow

Pathway through kidney 1000-2000L of blood flow through a day 180 L of water a day Urinate only 1.5 L per day Reabsorb glucose, aa, vitamins & water Excrete wastes, harmful substances, H+ & water Maintain homeostasis (blood volume, pH electrolytes & BP)

Regulation diagram

Closer look Proximal tubule Most nutrients reabsorbed to blood NaCl, H2O, HCO3-1 reabsorbed to blood NH3, H+1 secreted into the tubule from blood

Bowman’s Capsule and Proximal Tubule

Closer look Loop of Henle Descending loop water is reabsorbed Ascending loop NaCl is reabsorbed Longer loop-more NaCl is absorbed

Closer look Distal tubule Regulation of K+1 & NaCl here Depends on body’s needs K+ is secreted into tubule NaCl reabsorbed into tubule

Loop of Henle and Distal Tubule

Closer look Collecting duct NaCl can be reabsorbed here Some urea diffuses out of tube Remaining filtrate passes as urine

Collecting Duct

Regulation diagram

Transport Proximal tubule Distal tubule Filtrate CORTEX Loop of Henle NaCl Nutrients H2O HCO3– H2O K+ NaCl HCO3– H+ NH3 K+ H+ Filtrate CORTEX Loop of Henle NaCl H2O OUTER MEDULLA NaCl NaCl Collecting duct Key Urea Active transport NaCl H2O Passive transport INNER MEDULLA

Regulation of kidney ADH (antidiurectic hormone) Vasopressin Released by posterior pituitary gland Released in response to increased solute concentration in plasma Dehydrated or eating salty foods Distal tubule/collecting duct become more permeable to water Decreases the amount of water in urine Reabsorbs more water

ADH Thirst Hypothalamus ADH Pituitary gland Distal tubule H2O reab- Osmoreceptors in hypothalamus trigger release of ADH. Thirst Hypothalamus Drinking reduces blood osmolarity to set point. ADH Pituitary gland Increased permeability Distal tubule H2O reab- sorption helps prevent further osmolarity increase. STIMULUS: Increase in blood osmolarity Collecting duct Homeostasis: Blood osmolarity (300 mOsm/L) (a)

Aquaporin water channel ADH ADH receptor LUMEN Collecting duct COLLECTING DUCT CELL ADH Second messenger cAMP Protein kinase A Storage vesicle Exocytosis Figure 44.19 ADH response pathway in the collecting duct Aquaporin water channel H2O H2O

Effect of ADH

Regulation of kidney Low blood volume Juxtaglomerular apparatus Tissue located near artery supplies blood to glomerulus Secretes renin (enzyme) Angiotensinogen to angiotensin I Angiotensin I to angiotension II Causes blood vessels to constrict Causes release of aldosterone

Regulation of kidney Aldosterone Released by the adrenal cortex Due to low sodium levels Due to low blood volume Stimulates distal tubules/collecting ducts to reabsorb sodium Chlorine & water follow Stimulates potassium to be excreted

Regulation of kidney Aldosterone Increases serum sodium levels Increases water (blood volume) Decreases serum potassium levels ACE inhibitor Blood pressure medication Blocks the affects of aldosterone

Aldosterone Liver Distal tubule Renin Angiotensin I Juxtaglomerular Angiotensinogen Renin Angiotensin I Juxtaglomerular apparatus (JGA) ACE Angiotensin II STIMULUS: Low blood volume or blood pressure Adrenal gland Aldosterone Increased Na+ and H2O reab- sorption in distal tubules Arteriole constriction Homeostasis: Blood pressure, volume

Regulation of kidney ANH (atrial natriuretic homone) Secreted by right atrium Due to increased blood volume Causes sodium/water to be released Lowers blood volume Opposes aldosterone

Problems Diabetes insipidus Lacks ADH Pituitary problem Increased urination Leads to dehydration & low BP Alcohol consumption Blocks ADH