BISC 101: Animal Biology

Animal Physiology

How the physical structures in an organism works (to sustain life)

• How they maintain homeostasis, respond to their environment, and perform essential functions (respiration, digestion, reproduction)

Main purposes of anatomy and physiology

Homeostasis and Reproduction

Which of these mammals have to eat more to support each gram of it’s tissue: a dog or a human?

The dog; it has a higher mass specific metabolic rate than humans (higher SA:V ratio than a human)

Surface Area to Volume Ratio

An organism’s size is linked to it’s metabolism

• Smaller animals, with a higher SA:V ratio will lose more heat to their surroundings (higher metabolic rate)

• Large animals, with lower SA:V ratio will lose less heat to their surroundings (lower metabolic rate)

4 strategies animals use to get food

• Suspension feeders - capture tiny particles/organisms from water

• Deposit feeders - feed on organic matter (bacteria, algae, etc.) buried within sediments

• Fluid feeders - absorbs liquids, often by sucking on them (ex. butterflies, leeches, etc.)

• Mass feeders - consume large pieces of food (meat, grass, etc.)

Major components of a homeostatic system

Maintains a homeostasis via a feedback loop

• Sensor - monitors the environment for changes (thermoreceptors, chemoreceptors, pH changes) and sends a signal to the integrator

• Integrator - control center that processes information for the sensor and compares the signal to a predetermined set point and decides if a response is needed

• Effector - receives a command from the integrator and carries out a response to bring the variable back to a set point (ex. muscles contracting to produce heat)

4 ways which animals exchange heat with the environment

• Conduction - heat transfer through direct contact; molecule to molecule

• Convection - heat transfer through the movement of fluids

• Radiation - heat transfer through electromagnetic waves

• Evapouration - heat transfer from a liquid during phase changes (liquid to gas)

What would happen if the epithelial cells in the gills of a shark are treated with ouabain (molecule that poisons Na+/K+ ATPase)

Na+ and Cl- cannot move out of the epithelial cells into the surrounding seawater; salt would build up in the sharks tissues

Epithelial Cells

Cells that form a protective layer on surfaces of the body, they help with…

• Protection - physical barrier against pathogens/environmental damage

• Secretion - secrete substances like mucus, hormones, and sweat

• Absorption - in the digestive tract, they absorb nutrients from the foods you eat

• Filtration - in the kidneys, they are involved in filtering waste from the blood

Partial Pressure

Pressure of a specific gas in a mixture of gases; depends on…

• Total pressure of the gas

• Fractional pressure of the gas

Lymphatic System

A circulatory system made up of lymph vessels, which helps drain excess fluid (lymph) from the capillaries back to circulation

In the blood, DPG shifts the oxygen-hemoglobin equilibrium curve to the right, how does this shift affect oxygen loading and unloading?

Right shift = decreased affinity for oxygen, DPG promotes release of oxygen from hemoglobin to tissues

What would happen to the resting potential of an axon if the potassium leak channels were blocked?

The resting potential will be less negative as potassium would be unable to leak out of the cell

What would happen if feedback inhibition fails in a hormone signaling pathway?

Hormone production would not stop and the signal/response would continue

What would be the consequence of treating a person with drugs that inhibit trypsin?

Trypsin will inhibit protein digestion and reduce amino acid absorption - this could lead to weight loss and muscle atrophy due to protein deprivation

Myasthenia gravis is a diease that develops in humans when the immune ystem produces proteins that bind with Ach receptors in the muscles and causes muscle weakness. Why?

If Ach receptors are covered, they cannot bind to Ach and become activated - this means the muscles would have trouble contracting

Phenotypic Plasticity 

The ability of an organism to change it’s appearance, behaviour, or physiology in response to a change in it’s environment (ex. elephants that grows up in hot climates developed strong muscles for flapping it’s ears)

Digestive System

1. Food is taken in (ingestion)

2. Food is broken down (digestion)

3. Nutrients are absorbed (reabsorption)

4. Waste is removed (excretion)

Ingestion 

Different (evolutionary) adaptations allow animals to access food

• Fluid feeder

• Suspension feeder

• Deposit feeder

• Mass feeder

Digestion

Process of breaking down food into smaller molecules that the body can absorb for energy, growth, and repair

Absorption

Absorption of nutrients, vitamins, minerals, and water through the small intestine

• Small diffusion distance (one cell width) between lumen and blood

• Huge surface at organ and cell level

• Transport proteins bring in nutrients from digestive tract and into blood

Excretion

Formation and elimination of feces

• Large intestine: colon and rectum

• Colon: form feces by absorbing additional water and compacting the wastes that remain

• Rectum: storage location for feces until it can be eliminated 

Mouth

Mechanical & chemical processing of food; break down of lipids & carbohydrates

• Salivary amylase - breaks down starch into simpler sugars

• Salivary (lingual) lipase - breaks down triglycerides (lipids)

Esophagus

Moves food from the mouth into the stomach through peristalsis; a series of muscle contractions that push the food downwards

• Salivary amylase from the mouth can continue working until the stomach acids inactivates it

• Lingual lipase is secreted by the tongue and continues working in the stomach

Stomach

Stores and breaks down food into a liquid mixture (chyme) before releasing it into the small intestine, the stomach acid helps kill microbes and denatures proteins for easier digestion

• Pepsin - breaks down proteins into smaller peptides

• Gastric lipase - breaks down fats (triglycerides) into fatty acids and monoglycerides

• Lingual lipase - breaks down triglycerides

Small Intestine

Main site of digestion and nutrient (vitamins, minerals, water) absorption; chyme from the stomach mixes with bile (from liver) and pancreatic juices and enzymes are secreted to finish breaking down macromolecules. Nutrients are absorbed into the bloodstream and lymphatic system

• Pancreatic amylase - breaks down starch into simpler sugars

• Pancreatic lipase - breaks down fats into fatty acids and monoglycerides

Large Intestine

Absorbs water and electrolytes (Na+/Cl-) from the remaining indigestible food, forms and stores feces before elimination (excretion) in the rectum

• gut bacteria helps break down some undigested material, which can be thought of as a form of enzymatic action; producing beneficial vitamins

Rectum

Stores feces until it’s ready to be excrete through the anus; when the rectum is full, stretch receptors signal the brain to trigger the defecation reflex

In mammals, where does most of the enzymatic breakdown of molecules occur?

Small intestine; enzymes secreted from the liver and pancreas (including digestive enzymes), plus any left-over enzymes from the mouth and stomach, are active in the small intestine

How are nutrients stored and used to fuel activity

• Carbohydrates - stored mainly as glycogen in the liver and muscles

  • during short-term or high-intensity activity; glycogen is broken into glucose for ATP production

• Lipids - stored as triglycerides in adipose tissues and muscle cells

  • during low to moderate intensity activity or rest; fats are broken into fatty acids and glycerol for aerobic ATP production

• Proteins - doesn’t store protein specifically for energy

  • during prolonged exercise or fasting; amino acids can be converted into glucose or used directly for energy

How do the small intestines maximize the rate of transfer of nutrients (across a surface) into the body?

• By enabling a continual gradient = (amount on one side - amount on the other side)

• Between two things close together = distance across

• Over a large area = surface area

Endotherm

Animals which create most of their own heat from metabolism (mammals and birds)

Ectotherms

Animals which receive heat primarily from external sources (reptiles, amphibians, and fish)

Adaptation used by endotherms living in cold environments

Circulatory system arranged in a countercurrent flow to minimize heat loss 

• ex. blood flowing in opposite directions (veins and arteries)

Countercurrent Exchange

Two fluids run in opposite directions in adjacent pipes

• Useful because they maintain a gradient between two fluids along the length of adjacent pipes

Concurrent Exchange

Two fluids (ex. blood and water) run in the same direction in adjacent pipes

Countercurrent Exchange in Kidneys

Ensures the production of concentrated urine

• Filtrate in the Loop of Henle runs in opposite directions of the blood capillaries directly beside it

• Descending limb is permeable to water, but impermeable to solutes

• Ascending limb is permeable to solutes, but impermeable to water

  • Allows for solutes and water to be transported back into blood from the Loop of Henle, resulting in more concentration of urine

Countercurrent Exchange in Limbs

Minimizes heat loss at the body’s extremities 

• Arteries and veins are located beside each other, but the blood flow is in opposite directions

  • Heat is transferred from the arteries to the veins

Osmoregulation

Process of maintaining a stable balance of water and salt concentration within an organism’s body fluids

Osmotic stress in water (osmoregulators)

Oceans & seas (saltwater/marine) - hypertonic

• Fish would lose water by osmosis, and gain salts (electrolytes) by passive transport 

• Drinks water (also contains electrolytes) as a result; pumps ions out

Lakes, ponds, rivers, (freshwater) - hypotonic

• Freshwater fish would gain water by osmosis, and lose salts (electrolytes) by passive transport

• Doesn’t drink water; excretes lots of water; bring in extra electrolytes (active transport across gills, or through eating)

Getting Na+ and Cl- out of a shark (salt excretion)

1. Na+ from epithelial cell into blood; K+ from blood/ECF into cell-

• ATP is required (primary active transport)

• Establishes a sodium concentration gradient (high in blood/ECF, low in cell)

2. Na+, Cl-, and K+ are transported from blood/ECF into epithelial cells

• ATP is required from concentration gradient (secondary active transport)

• Brought Cl- into the cell - cell now have high [Cl-]

3. Cl- moves into ocean from cell, K+ moves into blood from cell

• No ATP (passive facilitated diffusion)

• Excreted Cl- which rebalanced K+ back into blood

4. Na+ diffuses from blood to ocean, between cells

• No ATP (simple diffusion)

• Na+ excreted

Kidneys

Where osmoregulation primarily occurs

• Renal artery - brings blood (with nitrogenous wastes) into kidneys

• Renal vein - carries blood (cleared of waste) away from kidneys

Kidney Pathway

1. Renal Corpuscle - filtration

2. Proximal Tubule - reabsorption of nutrients, vitamins, salts, water

3. Descending Loop of Henle - reabsorption of water (using osmotic gradient)

4. Ascending Loop of Henle - reabsorption of salts (making osmotic gradient)

5. Distal Tubule - reabsorption (when Na+ low)

6. Collecting Duct - combining from multiple nephrons; reabsorption of water (if dehydrated)

Renal Corpuscle

• Blood enters and filtration occurs as it passes through

  • Proteins, cells, and other large components of blood do not fir through the pores and do not enter nephron (stay in blood)

• Once filtered, the fluid is now known as pre-urine (filtrate)

Proximal Tubule

• Filtrate contains water and small solutes (urea, glucose, amino acids, vitamins, electrolytes)

• Almost all nutrients (& most of the NaCl and water filtered by renal corpuscle) are reabsorbed here

Loop of Henle

Reabsorption of water and salt (Na+/Cl-) using an osmotic gradient

• Descending limb - water reabsorbed (aquaporins), using salt gradient

• Ascending limb - Na+ and Cl- reabsorbed, using and making salt gradient

Distal Tubule

• Reabsorption may continue (K+ and H+ from blood may move into distal tubule)

• Filtrate that enters the distal tubule is always dilute

Collecting Duct

More water reabsorption, especially if dehydrated

• ADH plays a role in the production of concentrated or dilute urine; part of a negative feedback loop (returning the system to a set point)

Respiration Pathway

1. Ventilation - Inhalation and Exhalation 

2. Diffusion (gas exchange across lungs/gills/trachea) - exchange of O2 and CO2 between the air in lungs’ alveoli and the blood

3. Circulation (not all animals have this) - the circulatory system pumps oxygenated blood to the body’s tissues and carries CO2 back to the lungs

4. Diffusion (into cells) - exchange of gases between the blood and the body’s cells

5. Cellular Respiration - creates usable energy in the form of ATP using glucose and O2

Pulmonary and Systemic Circulation

Pulmonary:

• Sends deoxygenated blood to the lungs to oxygenate it

• From lungs to heart

• Uses pulmonary arteries and veins

Systemic:

• Sends oxygenated blood to organs and tissues

• From heart to body

• Uses aorta, arteries, veins, and capillaries

Movement of air in the body

1. Nose/Mouth - air enters the body

2. Pharynx (throat) - a passageway that connects the nasal and oral cavities to the larynx and esophagus

3. Larynx (voice box) - protects the airway during swallowing by using the epiglottis to block food from entering the trachea 

4. Trachea (windpipe) - reinforced with cartilage; main function is to provide passage from the larynx to bronchi for air to pass

5. Bronchi - trachea divides into two main tubes, left and right bronchi; carries air into the lungs

6. Bronchioles - in the lungs, bronchi branch into smaller tubes called bronchioles that brings air through tiny ducts and into elastic air sacs (alveoli)

7. Alveoli - where gas exchange occurs; O2 inhaled from air diffuses into capillaries and attaches to red blood cells, while CO2 moves from the capillaries to alveoli to be exhaled (removed)

Inhalation

• Diaphragm contracts and moves down

• Intercostal muscles contracts - ribcage moves up and out

• Increases chest cavity volume and decreases pressure to draw air into the lungs

Exhalation

• Diaphragm relaxes and moves up

• Intercostal muscles relax - ribcage moves down and in

• Decreases the chest cavity volume and increases the pressure to push air ut of the lungs

Why would it be beneficial to breathe more heavily on a mountain top?

The partial pressure of oxygen in the air is lower than at sea level

• Partial pressure is the pressure of a particular gas in a mixture of gases

Gas exchange in aquatic animals

1. Water flows in through the mouth, and out through the operculum (stiff flap of tissue covering the gills)

2. Gill filaments

3. Lamellae

4. Oxygenated blood

5. Deoxygenated blood

How is gas exchange of fish gills supported by it’s structures?

A - area for gas exchange

• Should be maximized

• Lots of surface area - capillaries and gills have huge surface area to volume ratio

D - diffusion distance

• Should be minimized

• Blood capillaries right next to the water, very short distance for diffusion

(P2-P1) - difference in partial pressure on either side of barrier

• Is maximized

• Blood and water are flowing in opposite directions; countercurrent exchange keeps a continual gradient over the whole gill

Do humans have respiratory structures for countercurrent exchange?

No; ventilation & gas exchange in our environment isn’t as challenging as under water

• Water - low oxygen (low PO2) and the fluid is heavy - harder to move around

• Air - lots of oxygen (high PO2) and the fluid is light - easier to move around

Gas Exchange - Movement of O2 and CO2

Depends on the partial pressure of O2 and CO2 in the body; gases will move via diffusion down their concentration gradients

• Lungs (higher concentration of O2 in lungs, higher concentration of CO2 in blood)

  • Net diffusion of O2 out of alveoli into blood

  • Net diffusion of CO2 out of blood into alveoli

• Tissues (higher concentration of O2 in blood, higher concentration of CO2 in tissues)

  • Net diffusion of O2 from the blood into tissues

  • Net diffusion of CO2 from tissues into blood

Role of Hemoglobin in Circulation

• O2 is transported through the blood via Hemoglobin

  • Hb has iron that binds to O2 - binding causes a conformational change in Hb, increases affinity for O2, allowing Hb to be saturated with O2

  • Amino groups of Hb bind CO2

• Hb reaches lungs - higher affinity for O2 due to high PO2

• Hb reaches tissues - lower affinity for O2 due to low PO2

  • 2,3 - DPG helps regulate release of O2

Other factors can affect Hb’s affinity for O2; resulting in shifts of the oxygen-hemoglobin dissociation curves

Oxygen-Hemoglobin Dissociation Curve

• Left shift - less oxygen being released

  • Increased affinity for O2

• Right shift - more oxygen being released

  • Decreased affinity for O2

How are O2 and CO2 carried in the blood?

• Most CO2; dissolved in the plasma, in the form of bicarbonate ions

• Most O2; bound to hemoglobin

Solutions:

• Convert CO2 into an ion that dissolves easily using Carbonic Anhydrase

• Bind O2 to a carrier protein, Hemoglobin

Hemoglobin carries & releases oxygen

• Tissues are actively respiring using up O2, so they have a lower blood PO2

• When O2 is bound to Hb, the O2 is stuck in the red blood cell - not accessible to the tissue that is actively respiring

• At the tissues, Hb needs to release O2 into the blood, so that it can diffuse into the cells there (so the cells can use it)

  • Hb picks up O2 when high amounts are present

  • Hb drops off O2 when low amounts are present

What happens to an O2-Hb dissociation curve in response to pH?

Bohr Effect

• Low pH deceases Hb’s ability to bind to oxygen

• In low pH environments, Hb unloads more O2

  • Shift to the right

• Provides the tissues with more oxygen so they can continue with cellular respiration

Bohr Effect vs. Root Effect

Bohr Effect (in mammals)

• Reduces O2 affinity - harder for Hb and O2 to bind in response to an increase in CO2 or decreased pH (acidic)

• Makes it easier to unload O2 into the tissues

Root Effect (in fish)

• Reduces both affinity and O2 carrying capacity in response to decrease in pH

• Builds up high O2 pressure in specific organs

2 main types of circulation

Closed Circulatory System

• Keeps blood inside a continuous network of vessels; blood is always contained within them

• Blood is separate from interstitial fluid

• High pressure; rapid blood flow

• Efficiently transports respiratory gases

Open Circulatory System

• Pumps blood (hemolymph) into open cavities to directly bathe organs

• Hemolymph mixes with interstitial fluid

• Low pressure; slow blood flow

• Does not transport respiratory gases efficiently

Directionalities

• Veins - towards heart

• Arteries - away from heart

• Deoxygenated - towards lungs

• Oxygenated - away from lungs

• Pulmonary Circulation - to and from lungs (including right atrium/ventricle); lower pressure

• Systemic Circulation - to and from body (including left atrium/ventricle); higher pressure

What would happen if one of the ventricles had thinner, less muscular walls?

It leads to a weakened ability to contract and pump blood effectively because it requires lots of pressure to move blood through the body

Why does the left ventricle have thicker walls?

It has to pump (oxygenated) blood to the entire body, which requires significantly more pressure than the right ventricle

Aldosterone

• A lipid (steroid)

• Hydrophobic and can cross the membrane

• Receptor is inside the cell

ADH

• A peptide

• Hydrophilic/polar and cannot cross the membrane

• Receptor is on the cell surface

Aldosterone and ADH effect on target cells in kidneys (osmoregulation)

Aldosterone saves sodium

• Distal Tubule: aldosterone increases amount of sodium transporters in membrane; sodium moves into blood

ADH saves water

• Collecting duct: ADH increases amount of aquaporins in membrane; more water can move passively into blood

Overall outcome

• Negative feedback to achieve homeostasis

  • An adaptation in your body, with systems that respond to keep your enzymes and systems happy

Digestion & absorption in the physiological response

Sensor (signal) - presence of food in digestive tract

Integrator - causes production/secretion of hormones into bloodstream

Effector (response) in small intestine - increase in the amount of digestive enzymes & relevant transporters

Types of blood vessels

Arteries

• Transports blood away from the heart under high pressure

  • Have thick, muscular, elastic walls to handle high pressure

Veins

• Transports blood towards the heart under low pressure

  • Have thinner, less muscular walls than arteries

Capillaries

• Allows for the exchange of gases and nutrients between blood and tissue

  • Have extremely thin, semipermeable walls for substances to diffuse in and out

Pathway of blood in heart

1. Deoxygenated blood enters from the superior/inferior vena cava into the right atrium

2. Deoxygenated blood moves from the right atrium, passing the tricuspid valve into the right ventricle

3. From the right ventricle, blood moves past the semilunar valve and out of the heart via pulmonary artery

4. Oxygenated blood comes back via pulmonary vein into the left atrium

5. From the left atrium, blood moves past the bicuspid valve into the left ventricle

6. Oxygenated blood flows into the aorta and blood is distributed to the rest of the body