Excretory System and Homeostasis (chpt 29)

Excretion

The removal of waste products of metabolism from the body

Homeostasis

The tendency to keep conditions in the body steady within certain levels (ie keep in equilibrium)

Organs of Excretion

• Skin: Excretes water, salt, and small amounts of urea in sweat from sweat glands. Controls temperature

• Lungs: Excretes water and carbon dioxide

• Urinary System: Excretes water and urea. Main organ of excretion and homeostasis for solution concentrations

Kidney Structure and Location

• Located on either side of spine at rear of upper abdominal cavity, below diaphragm. Left kidney slightly higher than right

• 3 layers, outer cortex, middle medulla, innermost pelvis

• Pelvis narrows and becomes ureter, connects to bladder, muscular bag stores urine, empties through urethra

• Kidney receives blood through renal artery, filtered, then leaves through renal vein into inferior vena cava

Kidney bodily fluids concentration control

• If lots of water drank, dilutes fluids in body, causing chemical reactions to slow. Body responds by producing large amounts of weak urine. Production of a lot of weak urine: diuresis

• If not a lot of water drank, fluids in body become too concentrated. Production of concentrated urine. Will also feel thirsty, body tries to bring body fluids concentration back to normal

Nephron Structure & Urine Formation

Urine formed by nephrons

1. Blood containing impurities enters kidneys (filters about 20% of blood that leaves heart)

2. Pressure of afferent arteriole and glomerulus increases greatly due to narrowing of blood vessels, especially in efferent arterioles. Forces fluid out through gaps between epithelial cells of capillaries in glomerulus in process of ultrafiltration, which happens in Bowman’s capsule

3. Resulting flomular filtrate passes through proximal convoluted tubule, all useful substances are reabsorbed (all except urea) by osmosis, diffusion, and/or active transport (depending on relative concentrations. Active transport: pumping substances against concentration gradient)

4. Cells of PCT have many miochondria to produce energy for active transport to pump substances back into blood against concentration gradient

5. More water reabsorbed in loop of Henle and distal convoluted tubule (DCT)

6. Final water balance → collecting duct, under influence of anti-diuretic hormone (ADH) aka vasopressin produced in pituitary

7. Urine psasses into pelvis through ureter into bladder. Sphincter muscle between bladder and urethra

What passes into Bowman’s capsule or not

• White blood cells, red blood cells, platelets, and most proteins → too big to pass through pore, so remain in blood. 20% of plasma passes into Bowman’s capsule, making blood thicker

• Ultrafication happens in Bowman’s capsule, liquid passed through capsule: glomerular filtrate. Contains glucose, amino acids, vitamins, salt, water, and urea. Collects there before going to proximal convoluted tubule (PCT). Urea is breakdown of excess amino acids in liver

Anti-diuretic hormone (ADH) action

• ADH makes collecting duct more permeable, so more water reabsorbed from urine into blood

• Production of large quantities of watery urine: diuresis. Antidiuretic hormone because presence stops diuresis

Ectotherms

Animals that have a body temperature that varies with the environmental temperature. Aka poikilothermic eg. all invertebrates, reptiles, amphibians, and fish. In mornings, may have to move to create heat

Endotherms

• Animal whose body temperature is independent of environmental temperature, aka homoeothermic

• Must monitor temperature of body, get rid of heat if temperature too high and produce and retain heat if temperature too low to keep temperature constant

• Temperature monitored and controlled by hypothalamus

When body too warm

• Sweat produced by sweat glands in skin through sweat ducts

• On skin surface, water evaporates, and since has high latent heat of vaporisation, cools skin. If breeze, cooling effect is enhanced

• Blood diverts towards skin’s surface when arterioles dilate, allowing more blood flow through capillary beds near surface of skin. Widening of arterioles called vasoldilaton. Allows more heat to escape by radiation. Makes skin red

• Hair lies flat on skin, erector muscle relaxed and thus no layer of insulating air is trapped, allows heat to escape

When body too cold

• No sweat produced, so no heat is lost

• Blood flow kept away from skin surface as arterioles supplying capillary beds constrict, narrowing of arterioles: vasoconstriction. Appear pale. If blood flow below a layer of subcutaneous fat, insulated

• Hairs stand erect when erector muscle contracts, thus trap a layer of insulatin gair, standing of erect hair: piloerection. Causes goosebumps

• Under normal conditions, liver, brain and muscles produce enough heat, however when cold, brain causes rapid contraction and relaxation of muscles, especially jaw: shivering. Produces heat

Skin structure and role

• Skin protects body. Kept supple by production of sebum from subaceous glands in hair follicles

• Without sebum, skin cracks, creating easy point of entry for pathogens. Sebum also makes skin waterproof and has antibacterial properties

• Layers of dead cells fall off taking pathogens with them. Skin also has own microflora of symbiotic microorganisms which outcompete pathogens

• Within skin, wandering phagocytic white blood cells to engulf antigens they may encounter

• Skin protects from ultraviolet radiation when melanocytes darken skin: tan