Homeostasis

Chapter 36 and section 31.3

Homeostasis

I. HomeostasisA. maintaining internal stability, regardless of external conditions

1. stability maintained for many variables2. cannot maintain stability for long in bad env. cond.

B. coordinated response of numerous body systems and parts of systems

C. keeps body within a range of variables that are conducive to lifeII. Feedback Mechanisms

A. feedback• result of a process affects the process itself

B. negative feedback 1. more common2. result inhibits further action at the start

C. positive feedback 1. result stimulates further action at the start2. often indicates a problem

An example of negative feedback

Fig. 31.10 Regulation of room temperature. An example of negative feedback.

Fig. 31.11 Regulation of body temperature. Another example of negative feedback.

III. ThermoregulationA. regulation of body temperature B. endotherms

1. maintain constant body temperature2. heat is generated internally through metabolic reactions3. tolerate a wide range of environmental conditions4. require a lot of food and energy5. major evolutionary adaptation6. preventing heat loss

a. shunting blood away from extremitiesb. countercurrent heat exchangec. fat reserves, hair, and feathersd. radiation and conductione. shivering

7. increasing heat lossa. shunting blood toward skin and resp. passagesb. radiation, convection, conductionc. evaporative cooling

8. behavioral, cellular, and hormonal means of thermoregulation

Heat exchange between an organism and its environment

C. ectotherms1. body temp. fluctuates with

environment2. heat is absorbed from

environment through a wide variety of behaviors• maintain fairly constant body

temp.3. requires less food and energy 4. cannot tolerate wide range of

environmental conditionsD. heterotherms

1. intermediate situation• endothermic or ectothermic

2. hummingbirds, bats, bees, etc.

Relationship between body temperature and ambient temperature in an ectotherm and endotherm.

IV. Osmoregulation and ExcretionA. osmoregulation

• regulation of water and ions within bodyB. excretion

• removal of metabolic wastes from bodyC. most metabolic wastes involve nitrogen – nitrogenous wastes

1. deaminationa. amino group (-NH2) removed from compounds toxic

ammoniab. ammonia is excreted or stored in some other form

2. typesa. fish = ammoniab. insects, birds, reptiles = uric acid (often a “paste”)c. other inverts., amphibians, mammals = urea + H2O urine

Fig. 36.1 Nitrogenous wastes

D. osmotic environments1. marine

a. ions diffuse into an animal’s body, water diffuses out• water conservation is biggest problem

b. ways animal can counteract thisi. must constantly drink seawaterii. osmoconformers• tissues become isotonic with surrounding water

iii. osmoregulators• salt actively transported out (salt-secreting cells)

2. freshwatera. water diffuses into an animal's body, ions diffuse outb. water conservation is not an issue, but retaining ions

is• do not drink freshwater

c. inverts.: flame cellsd. verts.: kidneys

3. terrestriala. chief problem is

obtaining and conserving water

b. inverts.: nephridia c. insects: Malpighian

tubulesd. verts.: kidneys

Fig. 36.4 Body fluid regulation in bony fishes

V. Human Excretory SystemA. structures involved

1. kidneys ureters urinary bladder urethra out of body2. renal artery and vein (renal circuit)

Fig. 36.7 The human excretory system

B. kidneys1. functions

a. filtrationb. reabsorption of water and other

useful ions • water conservation

c. tubular secretiond. excretion

2. structure a. cortex, medulla, renal pelvisb. nephrons • mostly in cortex

c. collecting ducts • mostly in medulla

Key function of excretory systems, an overview

Fig. 36.8 Macroscopic and microscopic anatomy of the kidney

C. nephrons1. actual filtering, functional units of kidneys

• urine formed here2. components

a. Bowman’s capsuleb. glomerulus • filtration occurs here

c. proximal tubulesd. looping tubule (Loop of Henle)e. distal tubules join with collecting ducts

3. nephrons empty into collecting ducts4. ducts pass through medulla empty into renal pelvis

ureter

Fig. 36.9 Nephron anatomy

5. reabsorption of water and other useful ionsa. takes place across the peritubular capillariesb. countercurrent exchange, osmosis, active/passive

transport6. excess water remains in nephrons and will be

excreted7. tubular secretion • excess ions/waste secreted from capillaries into

nephrons

Fig. 36.11 Processes in urine formation

D. control of nephron function1. antidiuretic hormone (ADH) controls water reabsorption

a. secreted by pituitary gland • under control of hypothalamus

b. ADH present H2O reabsorbedc. ADH absent H2O excreted

2. aldosterone controls salt reabsorptiona. secreted by adrenal glands b. high levels of aldosterone increase in reabsorption of salt• salt used to keep blood 0.9% saline (isotonic)

homeostasis!c. also promotes excretion of K+ ions

3. atrial natriuretic hormone (ANH) promotes excretion of salt and Na+