MCAT Biology - Homeostasis

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Ibuprofen

nonsteroidal anti-inflammatory drug; analgesic; can cause analgesic nephropathy

dialysis

performs filtration to purify the blood and excrete wastes externally, a crucial function that the kidneys would normally perform

excretory system

regulation of blood pressure, blood osmolarity, acid–base balance, and removal of nitrogenous wastes

kidneys

two bean-shaped structures located behind the digestive organs at the level of the bottom rib

nephron

functional unit of the kidney; approx. 1 million per kidney

ureter

nephrons eventually empty into this tube in the renal pelvis towards the bladder

bladder

storrs urine for later excretion

urethra

tube through which urine exists the body

renal cortex

kidney’s outermost layer; isotonic to blood

renal medulla

sits within kidney; deeper than cortex; isotonic to 4x concentration of blood

renal hilum

deep slit in the center of a kidney’s medial surface

renal pelvis

widest part of the ureter; spans almost the entire width of the renal hilum

renal artery

branches out, passes through the medulla, and enters the cortex as afferent arterioles through the renal hilum

renal vein

exit through the renal hilum

portal system

consists of two capillary beds in series through which blood must travel before returning to the heart

glomerulus (pl. -i)

highly convoluted capillary tufts derived from afferent arterioles in the nephrons

afferent arterioles

carry blood to the glomerulus

efferent arterioles

carry blood away from the glomerulus

vasa recta

capillary bed around the loop of Henle

Bowman’s capsule

cup-like structure around the glomerulus that leads to a long tubule with many distinct areas

detrusor muscle

muscular lining of bladder; parasympathetic activity causes the detrusor muscle to contract

internal urethral sphincter

smooth muscle; contracted in its normal state; under involuntary control

external urethral sphincter

skeletal muscle; under voluntary control

stretch receptors

convey to the nervous system that the bladder requires emptying, causes parasympathetic neurons to fire

micturition reflex

Stretch receptors signal for the detrusor muscle contracts and the internal sphincter to relax when bladder is full; disspates in a few minutes if urge not sated but will begin again

Urination

facilitated by the contraction of the abdominal musculature, which increases pressure within the abdominal cavity, resulting in compression of the bladder and increased urine flow rate

filtration

approximately 20 percent of the blood that passes through the glomerulus is filtered as fluid into Bowman’s space

filtrate

collected fluid in Bowman’s space; similar in composition to blood but does not contain cells or proteins

Starling forces

account for the pressure differentials in both hydrostatic and oncotic pressures between the blood and Bowman’s space

hydrostatic pressure of glomerulus higher than Bowman → osmotic pressure opposes but is weaker

kidney stone

blocks ureter; buildup of urine; may reverse Starling forces

secretion

nephrons put salts, acids, bases, and urea directly into the tubule by either active or passive transport

Ammonia (NH3)

byproduct of the metabolism of nitrogen-containing compounds; highly basic so can disturb the pH of blood and cells

urea

what the liver converts ammonia to; travels to the kidney and is secreted into the nephron for excretion in the urine

reabsorption

Some compounds that are filtered or secreted may be taken back up for use

proximal convoluted tubule (PCT)

filtrate first enters; stays isotonic to the interstitium

reabsorbed: water, amino acids, glucose, water-soluble vitamins, and the majority of salts → picked up by vasa recta

secreted: hydrogen ions, potassium ions, ammonia, and urea

interstitium

connective tissue surrounding the nephron

descending limb of the loop of Henle

dives deep into the medulla; permeable only to water; creates interstitium gradient to maximise reabsorption

reabsorbs: water

countercurrent multiplier system

flow of filtrate through the loop of Henle is in the opposite direction from the flow of blood through the vasa recta

(think gills!)

ascending limb of the loop of Henle

climbs up from the medulla; permeable only to salts; creates interstitium gradient to maximise reabsorption

reabsorbs: salts

diluting segment

while ascending to the outer medulla, the loop of Henle becomes thicker because the cells lining the tube are larger; contain large amounts of mitochondria, which allow the reabsorption of sodium and chloride by active transport; only portion of the nephron that can produce urine that is more dilute than the blood

distal convoluted tubule (DCT)

responds to aldosterone

reabsorbs: sodium (water follows sodium)

secretes: hydrogen ions, urea, ammonia, potassium ions

edema

body accumulates excess fluid in the lungs or peripheral tissues

Collecting Duct

responsive to aldosterone and ADH

reabsorbs: water and sodium

urine

mostly urea, uric acid, and excess ions (sodium, potassium, magnesium, and calcium); flows through the ureter to the bladder where it is stored until voiding

Aldosterone

steroid hormone that is secreted by the adrenal cortex in response to decreased blood pressure

renin

released from juxtaglomerular cells in kidney with decreased blood pressure

angiotensinogen

liver protein; cleaved by renin → angiotensin I

angiotensin I

metabolized by angiotensin-converting enzyme in the lungs → angiotensin II

angiotensin-converting enzyme

angiotensin I → angiotensin II

angiotensin II

promotes the release of aldosterone from the adrenal cortex

Antidiuretic hormone (ADH, vasopressin)

peptide hormone synthesized by the hypothalamus and released by the posterior pituitary in response to high blood osmolarity; directly alters the permeability of the collecting duct, allowing more water to be reabsorbed by making the cell junctions of the duct leaky

inhibited by alcohol and caffeine

osmotic pressure

“sucking” pressure that draws water into the vasculature caused by all dissolved particle

Oncotic pressure

osmotic pressure that is attributable to dissolved proteins specifically

average blood osmolarity

maintained at approximately 290 milliosmoles (mOsm) per liter

bicarbonate buffer system

major regulator of blood pH

skin (integument)

largest organ in our bodies by both weight and size; one of the major components of nonspecific immune defense, protecting us from exposure to the elements and invasion by pathogens; derived from the ectoderm

hypodermis (subcutaneous layer)

layer of connective tissue that connects the skin to the rest of the body; contains fat and fibrous tissue

dermis

middle layer of skin

epidermis

most superficial layer of skin; subdivided into strata

strata

layers of the epidermis

• stratum basale (deepest)

• stratum spinosum

• stratum granulosum

• stratum lucidum

• stratum corneum (shallowest)

reverse: Come, Let’s Get Sun Burned

stratum basale

contains stem cells and is responsible for proliferation of keratinocytes

keratinocytes

the predominant cells of the skin, that produce keratin

keratin

protein; resistant to damage and provides protection against injury, water, and pathogens

ex. hair, fingernails, calluses

stratum spinosum

cells become connected to each other; also the site of Langerhans cells

stratum granulosum

keratinocytes die and lose their nuclei

stratum lucidum

present in thick, hairless skin, such as the skin on the sole of the foot or the palms, and is nearly transparent

stratum corneum

contains up to several dozen layers of flattened keratinocytes, forming a barrier that prevents invasion by pathogens and that helps to prevent loss of fluids and salt

Calluses

form from excessive keratin deposition in areas of repeated strain due to friction; they provide protection to avoid damage in the future

Melanocytes

found in the stratum basale; derived from neural crest cells; produce melanin; same number in everyone but different activity; increase activity in response to UV light

melanin

pigment that serves to protect the skin from DNA damage caused by ultraviolet radiation; produced in melanocytes and transferred to keratinocytes

albinism

genetic (autosomal recessive) metabolic disorder characterized by the inability to synthesize melanin

vitiligo

autoimmune disorder in which melanocytes are killed by the individual’s immune system

Langerhans cells

special macrophages that reside within the stratum spinosum; capable of presenting antigens to T-cells in order to activate the immune system

papillary layer

upper layer of dermis; consists of loose connective tissue

reticular layer

lower layer of dermis; denser; sweat glands, blood vessels, hair follicles, sensory receptors

Merkel cells (discs)

sensory receptors present at the epidermal–dermal junction; responsible for deep pressure and texture sensation

free nerve endings

respond to pain

Meissner’s corpuscles

respond to light touch

Ruffini endings

respond to stretch

Pacinian corpuscles

respond to deep pressure and vibration

Thermoregulation

control of internal temperature

Sweating

excellent cooling mechanism that is controlled by the autonomic nervous system; Postganglionic sympathetic neurons that utilize acetylcholine innervate sweat glands and promote the secretion of water with certain ions onto the skin; Heat is then absorbed from the body as the water molecules undergo a phase change to evaporate

piloerection

arrector pili muscles contract, causing the hairs of the skin to stand up on end; trap a layer of heated air near the skin

Shivering

Skeletal muscle contracts rapidly; requires a sizeable amount of ATP

white fat

layer of fat just below the skin; helps to insulate the body

brown fat

much less efficient electron transport chain, which means that more heat energy is released as fuel is burned