Topic 11.3 The Kidney & Osmoregulation

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

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

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

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

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

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

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.

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

Glomerulus

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

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

Loop of Henle

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

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)

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

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

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

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