Bio 1.10 Homeostasis [Excretory system and Skin]

Excretory system

functions to regulate blood pressure, blood osmolarity, acid-base balance and removal of nitrogenous waste

kidney

produces urine

which flows into the ureter at the renal pelvis. Urine is then collected in the bladder until excreted through the urethra

contain a cortex and hilum which contains renal artery, renal vein and ureter.

portal system [kidney]

2 capillary beds

• blood from the renal artery flows into afferent arterioles which form glomeruli in the bowman’s capsule (1st capillary bed)

• blood then flows through the efferent arteriole to the vasa recta (second capillary bed) which surround the nephron before leaving the kidney through the renal vein

bladder

detrusor muscle (muscular lining) under parasympathetic control

• internal urethral sphincter

• external urethral sphincter

internal urethral sphincter

consist of smooth muscle, under involuntary (parasympathetic control)

external urethral sphincter

consists of skeletal muscle, under voluntary control

3 solute movement processes [kidney]

• filtration

• secretion

• reabsorption

filtration

movement of solutes from blood to filtrate at bowman’s capsule

direction and rate of filtration is determined by starling forces, which accounts for the hydrostatic and oncotic pressure differentials between the glomerulus and bowman’s space

secretion

movement of solutes from blood to filtrate anywhere other then bowman’s capsule

reabsorption

movement of solutes from filtrate to blood

Proximal convoluted tubule

site of bulk reabsorption of glucose, amino acids, soluble vitamins, salt and water.

site of secretion for hydrogen ions, potassium ions, ammonia and urea

descending loop of henle

permeable to water but not salt

filtrate moves into the more osmotically concentrated renal medulla, water is reabsorbed from the filtrate.

vasa recta and nephron flow in opposite directions creating a countercurrent multiplier system that allows maximal absorption of water

ascending loop of Henle

permeable to salt but not water

salt is reabsorbed both passively and actively.

the diluting segment is in the outer medulla, because salt is actively reabsorbed in this site, the filtrate actually becomes hypotonic compared to blood.

distal convoluted tubule

responsive to aldosterone and is a site of salt reabsorption and waste product excretion like the PCT

Collecting duct

responsive to both aldosterone and antidiuretic hormone and has variable permeability which allows reabsorption of the right amount of water depending on the body’s needs

aldosterone [steroid hormone]

regulated by the renin-angiotensin-aldosterone system

that increases sodium reabsorption in the DCT and collecting duct thereby increase water reabsorption.

results in increase blood volume and pressure [no change in blood osmolarity]

kidney can regulate PH by selective reabsorption or secretion of bicarbonate or hydrogen ions

skin

acts as a barrier protecting us from elements and invasion by pathogens

prevents dehydration and salt loss from the body

3 major layers of the skin

• epidermis (top)

• dermis

• hypodermis

5 layers of the epidermis

• stratum basale

• stratum spinosum

• stratum granulosum

• stratum lucidum

• stratum corneum (top)

stratum basale

contains stem cells that proliferate to form keratinocytes

melanocytes

produce melanin which protects the skin from DNA damage by ultraviolet radiation

melanin is passed to keratinocytes

langerhans cells

special macrophages that serves as antigen-presenting cells in the skin

dermis

• papillary layer

• reticular layer

sensory cells located in the dermis

• merkel cells (deep pressure and texture)

• free nerve endings (pain)

• Meissner’s corpuscles (light touch)

• rufffini endings (stretch)

• pacinian corpuscles (deep pressure and vibration)

hypodermis

contains fat and connective tissue

also connects the skin to the rest of the body

vasodilation

cooling mechanism,

eg sweating, sweat glans innervated by postganglionic cholinergic sympathetic neurons

vasoconstriction

piloerection, arrector pili muscles contract casuing hairs to stand

shivering and insulation provided by fat

renin-angiotensin-aldosterone system (RAAS)

a crucial hormone system that regulates blood pressure, fluid, and electrolyte balance by controlling sodium and water reabsorption, vascular tone, and the release of aldosterone