Physiology Exam 1 (Mizzou) 3202 MPP

Homeostasis

it is the constancy of the internal environment that is the condition for a free and independent life

homeostasis: control

receptors

integrating center

effectors

signals

Receptors

thermoreceptors

chemoreceptors

baroreceptors

Integrating Center

orchestrates an appropriate response many integrating centers are found in the brain

Effectors

responsible for body responses

- muscles (smooth, striated, and cardiac)

- glands

Signals

input signal is from a receptor to an integrating center

output signal is from an integrating center to an effector

chemical or nerves

Negative Feedback

- response opposes or removes the signal

- can restore normal state, but cannot prevent initial signal

- designed to keep system at / near a set point so that the regulated variable is relatively stable

- can restore normal state

Positive Feedback

response reinforces the stimulus

- not homeostatic

- the stimulus is increased

Intrinsic

within organ

- ability of vessels to constrict or dilate

Extrinsic

regulation by nervous or endocrine (hormone) systems

-

Antagonistic Effectors

many factors (blood glucose, heart rate) are controlled by multiple effectors, which have antagonistic actions

- refined control

Blood pressure (negative feedback response)

- lying down

- standing up (blood pressure falls) stimulus

- blood pressure receptors respond (sensor)

- medulla oblongata of brain

- heart rate increases (effector)

- rise in blood pressure

Homeostasis: Mass Balance

- depends on body maintaining mass balance (amount of substance in the body to remain constant, any gain must be offset by an equal loss)

- total amount = intake + production - excretion - metabolism

- clearance = the rate a which a compound disappears from blood

Homeostasis: Fluid Compartments

ICF = intracellular fluid (fluid within cells)

ECF = extracellular fluid (fluid outside cells but within body is the "internal environment')

- subdivisons

- plasma: fluid around blood cells

- tissue fluid: fluid surrounding other cells

Fluids

- intracellular fluid is 2/3 of body volume inside of our cells

- fluid moving inside and outside ICF must cross cell membrane

- extracellular fluid - fluid outside of cells (1/3 of body volume)

- the ECF consists of interstitial fluid and plasma

- interstitial fluid = lies between circulatory system and cells (75% of ECF volume)

-plasma = fluid matrix of blood (25% of ECF)

Ion Concentration

free calcium is toxic to cells

- calcium is required tho

Extracellular Environment

everything outside the cells

- receive nourishment from and release wastes into extracellular environment

- cells communicate with each other by secreting chemical regulators into the extracellular environment

- lots of protein (collagen) connecting fibers

- elastin protein fibers contract or relax its stretchy

Extracellular Matrix

- contains protein fibers (collagen)

- ground substance (glycoproteins and proteoglycans)

- Integrins = glycoproteins that extend from the cell and bind to the extracellular matrix: cells have ability to move

Cell Membrane

-lipid rich environment

-hydrophilic (heads) on outside they love water

- hydrophobic (tails) on the inside hate water

- proteins aren't fixed in the membrane they move and aggregate (cluster together)

- channels and pores to help stuff get into and out membrane

- cholesterol provides flexibility

- cells can change shape

Cell Membrane: Function

- physical isolation

- regulation of exchange with the environment

- communication between the cell and its environment

- structural support

Solubility

- how much we can put in there

solute (sugar, salt) dissolved in solvent (water)

Epithelial Tissue: Structure

- all surfaces of our body

- any substance that enters or leaves the internal environment must cross and epithelium

- two types

layering

- simple or stratified

shapes

- squamous, cuboidal, columnar

function

- exchange, transporting, ciliated, protective, secretory

Epithelial Transport

Absorption

transport of digestive products across intestinal epithelium into the blood

reabsorption

transport of molecules out of the urinary filtrate back into the blood

transceullular transport

movement of molecules through the cytoplasm of molecules through the cytoplasm of epithelial cells

paracellular transport

movement across the tiny gaps between cells

Cell-Cell Adhesion

paracellular transport is limited by cell-cell adhesion

Gap junctions

allow adjacent cells to pass ions and regulatory molecules through a channel between the cells

paracrine signaling

cells within an organ secrete molecules that diffuse across the extracellular space to nearby target cells

synaptic signaling

involves neurons secreting neurotransmitters across a synapse to target cells

endocrine signaling

glands that secrete hormones into the bloodstream

- multiple target cells

- every cell is going to see it

Receptors

target cell receives a signal because it has a receptor proteins specific to it on the plasma membrane or inside the cell

Affinity

a measure of how well a ligand binds to the receptor (how strong the signal wants to bind to the receptor)

Agonist

chemical that binds to and activates a receptor

antagonist

chemical that binds to a receptor and blocks/inhibits response

Plasma membrane transport

- selectively permeable

- not permeable to proteins, nucleic acids, or large molecules

-permeable to ions, nutrients, and wastes

Passive transport

molecules move from higher to lower concentration without using metabolic energy

Active Transport

molecules move from lower to higher concentration using ATP and specific carrier pumps

Diffusion

-don't need ATP

-high to low concentration

-net movement until concentration is equal

-rapid over short distances

-directly related to temp

-inversely related to molecular weight and size

Diffusion: Plasma Membrane

small, non-polar (or uncharged) lipid-soluble molecules pass easily through the lipid portion of the membrane

- water can pass through using special channels called aquaporins (osmosis)

Channels: Plasma Membrane

- charged ions can pass through ion channels

- larger molecules can not pass through the membrane by simple diffusion (special carrier proteins)

Facilitated Diffusion

powered by the random movement of molecules

- no ATP used

- high to low concentration

- requires specific carrier proteins

- transport proteins may always exist in the plasma membrane

Osmosis

water molecules = no charge, so pass through membrane slowly

- aquaporins are found in kidney, eyes, lungs, salivary glands, and the brain

- solutes that cannot cross and permit osmosis are called osmotically active

Osmotic Pressure

force surrounding a cell required to stop osmosis

- higher solute concentration, requires higher osmotic pressure

- pure water = 0

Osmolality

the total molality of a solution when you combine all of the molecules within it

Carrier-Mediated Transport

-large or polar cannot diffuse across membrane (amino acids, glucose)

- carrier proteins move them across membrane

- characteristics:

- specific to molecule

- competition for similar carriers or molecules

- saturation (# of carriers is limited)

Primary Active Transport

- hydrolysis of ATP is directly responsible for carrier protein function

- transport protein = ATPase enzyme (hydrolyze ATP)

- pump activated by phosphorylation

Sodium Potassium Pump (Na+/K+ Pump)

- found in all body cells

- 3 Na+ out of the cell and 2 K+ into the cell

FUNCTIONS:

- provides energy for coupled transport of other molecules

- produces electrochemical impulses in neuron and muscle cells

- maintains osmolality

Secondary Active Transport

- moving sodium back into the cell gives molecules energy

- Sodium pumped out of cell using ATP (active transport)

Cotransport or symport

other molecule moved with sodium

- common way to transport glucose

Countertransport or antiport

the other molecule is moved in the opposite direction from sodium

Bulk Transport

- exocytosis

- endocytosis

Exocytosis

large molecules; proteins, hormones, and neurotransmitters secreted

- involves fusion of a vesicle with plasma membrane

- requires ATP

Endocytosis

- large molecules (cholesterol)

- usually a transport protein interacts with plasma membrane proteins to trigger

Digestive System

- processing of ingested food and delivery of nutrients

- large immune organ

- largest habitat for microflora

- critical role in immune defense

Storage and Elimination

temporary storage of ingested food and subsequent elimination of undigested material

Immune Barrier

- simple columnar epithelium with tight junctions prevents swallowed pathogens from entering body

- immune cells in connective tissue of the tract promote immune responses

Ingestion

taking food into the mouth

Mastication

chewing and mixing food with saliva

- large pieces of food --> chewing --> smaller pieces that mix with saliva, which contains mucus, antimicrobial agents & salivary amylase to start carbohydrate digestion

Deglutination

swallowing

oral: voluntary; muscles of mouth and tongue mix food with saliva to form a bolus

Pharyngeal: involuntary

- uvula (soft palate) lifts to cover nasopharynx, and epiglottis covers vocal cords

- upper esophageal sphincter relaxes

- esophageal: automatic; controlled by swallowing center of brain stem; bolus --> esophagus --> stomach (peristalsis)

peristalsis

wave-like, one way movement through tract

segmentation

churning and mixing while moving forward

exocrine

digestive enzymes, hydrochloric acid, mucus, water, and bicarbonate

endocrine

hormones that regulate digestion

digestion

break food down into smaller units via both physical and chemical actions

absorption

transport of digestion products (nutrients) into blood or lymph

Digestive System

- one way transport

- salivary glands important - mix things up

- liver / gallbladder (absorption of fat)

- pancreas (exocrine function and endocrine function)

- we need digestive enzymes

Parasympathetic Nervous System (extrinsic regulation)

- "rest and digest"

- stimulates esophagus, stomach, small intestine, pancreas, gallbladder, and first part of large intestine via vagus nerve

- spinal nerves in sacral region stimulate lower large intestine

Sympathetic Nervous System (extrinsic regulation)

- "flight or fight"

- inhibits peristalsis and secretion

- stimulates contraction of sphincters

Intrinsic regulation

sensory neurons in gut wall help via enteric nervous system

- paracrine signals

Intestinal Contraction and Motility

- moves chyme aborally (forward) from mouth --> anus

- mixes chyme with digestive secretions

- breaks chyme into small particles, surface area up

- smooth muscle contractions occur automatically due to endogenous pacemaker activity

peristalsis

primary: initiated in esophagus by swallowing

secondary: initiated by distension

step 1- contraction of circular muscles behind food mass

step 2 - contraction of longitudinal muscles ahead of food mass

step 3 - contraction of circular muscle layer forces food mass forward

Fluid and Electrolyte: Secretion & absorption

- most fluid doesnt come from what we drink it comes from (bile, saliva, pancreas secretion)

- at the end we want to get the fluid back

- hold back in small intestines

Stomach

-stores food, breaks it into smaller pieces

- churns food to mix with gastric secretions - this mixture is now chyme

- begins protein digestion

- kills bacteria in the food (acid)

- moves chyme into small intestine

- highly acidic around 2 (most things don't live well)

- immunoprotective function

Gastric Pits & Gastric Glands

mucus cell - secrete mucus

parietal cell - secrete acid (hydrochloric acid)

chief cell - secrete pepsinogen (important digestive enzyme) inactive form

- don't want to auto digest

Parietal cells

- how we regulate pH in the body and kidney

- bicarbonate helps with pH in blood

- secrete out hydrogen

- primary active transport

Functions of HCI

creates acidic environment in stomach --> pH 1-2

- ingested proteins are denatured (allows enzymes access)

- pepsinogen is concerted to active pepsin (digest proteins)

- serves as the optimal pH for pepsin

Pepsin

catalyzes hydrolysis of peptide bonds ingested proteins

Stomach: Digestion and Absorption

- proteins being digestion in the stomach

- salivary amylase is not active at pH 2, so this activity stops in the stomach

- alcohol and NSAIDs (aspirin) are the only common substances absorbed in the stomach (high lipid solubility)

Small Intestine

most digestion occurs here

- carried out by pancreatic, intestinal enzymes

- all exocrine secretions enter at the duodenum

- whatever is in this tract is external to us

- complete digestion of carbs, proteins and fats

Large Intestine

-absorption of water, electrolytes, vitamin K and some vitamin B

- production of vitamin K and B vitamins via microbial organisms

- habitat for microflora

- storage / processing of feces

Cephalic Phase

-short duration, prepares stomach for arrival of food before ingestion

-direct neural stimulation of acid, mucus, enzyme secretion

Gastric Phase

-vagal reflexes stimulates acid secretion and gastrin release

- local release of histamine (stimulates acid secretion) triggered by stretch

Intestinal Phase

-long duration

- controls gastric emptying rate

- limits gastric acid secretion

- optimize conditions for enzymatic digestion

Gastrin (stomach)

stimulates parietal cells to secrete hydrochloric acid

- stimulates chief cells to secrete pepsinogen

- maintains structure of gastric mucosa

Secretin (small intestine)

- water & HCO3- secretion from pancreas

- raises pH of incoming chyme --> allows pancreatic enzymes to be active

Cholecystokinin (CCK) (Small Intestine)

- stimulates contraction of gallbladder

- pancreatic enzyme secretion

- tells pancreas to dump digestive enzymes, then feeds back to the stomach to tell it to stop

Digestion & Absorption

- digestion breaks polymers into monomer building blocks

- absorption takes these monomers into the bloodstream to be used by the cells

Carbs: Digestion

most carbs ingested as starch or sugars

- starch = mouth

- no digestion in the stomach - too acid

- cont in intestines = pancreatic amylase

- brush border enzymes = break down disaccharides

Protein: Digestion & Absorption

begins in stomach with pepsin and HCI (produce short chain polypeptides)

- finishes in duodenum and jejunum with pancreatic trypsin

Fat: Digestion & Absorption

- digestion begins in duodenum: bile stabilizes fat emulsion and lipase (from pancreas) breaks it down into fatty acids and glycerol

Fat: Emulsification and Digestion

- youtube video

Fat: Absorption & Transport

- youtube video

Fat Soluble Vitamins (A,D,E,K)

absorbed with fat

Water-soluble vitamins (C, most B vitamins)

carrier-mediated transport

Vitamin B12

- requires gastric-secreted intrinsic factor uptake by enterocytes in terminal ileum

- IF is produced and secreted into the stomach by parietal cells

Regulation of Pancreatic and Bile Secretion

- youtube video

Enterohepatic Circulation

recycling of bile salts regulates hepatic synthesis of bile acids from cholesterol, and therefore, controls plasma cholesterol levels

- 95% of bile salts are recirculated

- whats absorb in intestinal tract goes back to liver

Pancreas: Exocrine Function

- exocrine function dumps out digestive enzyme into intestine (inside of our body to out)

- sweat is one example

- don't want active proteases

- zymogen is a pro enzyme