BISC 101 Test 2

Physical constraints

Physical constraints

• Climate, temperature, aquatic vs terrestrial environments, common competition, other animals, etc.

Higher surface area to volume =

Better exchange of materials with environment. Larger animals have low surface area: volume ratio due to slower metabolism

Physiological response

e.g. Hot temperature outside, so an elephant flaps its ears

Phenotypic Plasticity

e.g. An elephant that grows up in a particular hot climate has developed strong muscles for flapping its ear

Adaptation

e.g. Elephants have lived for generations in hot climates. They have evolved broad, thin ears

Homeostasis

Stability in the chemical and physical conditions of an organism’s cell, tissues and organs

Homeostasis Negative Feedback Loop

• Sensors measure a variable (Temp raised to 39 C)

• Integrator compares this input to the current set point (37 C)

• Effectors act to return body to set point (lower to 37 C)

  • The feedback is the reverse of the stimulus/ trigger

Endotherms

Animals which create most of their own heat and metabolism

Ectotherms

Animals which receive heat primarily from external sources

Endotherms Pros and Cons

Pros: consistently ideal temperature for active lifestyle, even when environment is cold

Cons: requires much more energy/food to fuel heat production

Ectotherms Pros and Cons

Pros: needs less food, and saves more energy for growth and reproduction

Cons: low activity levels and metabolism when too cold

Heterothermic

Organisms that are able to maintain different temperatures in different regions. Ex: Bees

Countercurrent flow

• Circulatory system arrangement to minimize heat loss (An adaptation to counter cold)

Why is countercurrent flow necessary?

Without it, lots of heat would be lost to the ground and cold venous blood would need to be re-warmed

How does countercurrent flow work?

Blood going to extremities is “pre-cooled” then venous blood heated by arterial blood. Arteries and veins are very close together, high SA exists for heat transfer, gradient exists along entire transfer surface

Factors in maximizing heat transfer

• A continual heat gradient/ big difference in temperature

• Distance between two things exchanging heat

• Surface area over which heat transfer is occurring

What challenges to osmoregulation do a marine fish, freshwater fish and terrestrial vertebrates face?

Marine fish: gains salt, lose water

Freshwater, lose salts, gain water

Terrestrial vertebrates: lose salts, lose water

Challenges of osmoregulation for Marine fish

• Hypertonic environment leads to water loss by osmosis

• Drinking/ eating brings excess salts

Solutions of osmoregulation for Marine fish

• Drinking large volumes of water replenishes water lost by osmosis

• Active transport of ions out of the body through gills removes excess salt

• Urine is very salty, very low in volume

Challenges of osmoregulation for Freshwater fish

• Hypotonic environment brings in excess water by osmosis

• Salts are lost by excretion

Solutions of osmoregulation of Freshwater fish

• Producing lots of dilute urine removes excess water

• Salts are actively transported into the body through bills

• Very little drinking

Challenges of osmoregulation of sharks

• Sharks are osmoconformers (isotonic to water), but regulate salt concentrations

• Maintaining lower NaCl concentrations than seawater

Solutions of osmoregulation of sharks

• Rectal gland secretes high concentration of Na+ and Cl- into rectum

  1. Na+/K+ pump: sets up Na+ gradient

  2. Co-transporter uses Na+ gradient to actively pump Cl- and K+

  3. Cl- and K+ channels remove ions by facilitated diffusion

  4. Na+ diffuses between cells into lumen

  5. Gland secretes Na+ and Cl- into rectum

Challenges of osmoregulation of terrestrial vertebrates

• Water lost by evaporation

• Salts lost through sweat

Solutions of osmoregulation of terrestrial vertebrates

• Drink/eat to replenish waters and salts

• Reabsorb water and salts in kidney

Kidney

• Effector for regulation of water, salt and pH balance

• Excretion for selective removal of nitrogenous wastes, toxins/ chemicals

Urine

Water, Urea + wastes, Excess acid, Excess salt

Nephron

• Blood filtered in the renal corpuscle

• Reabsorption/ secretion in proximal tubule, loop of Henle, distal tubule. optimizes water and solute concentrations

• Urine excreted via the collecting duct

• Purpose is to recapture nutrients, salts and water

Renal corpuscle - Filtration

• Capillaries in the glomerulus have large poles

• Blood pressure causes water and small solutes (filtrates) to seep out, into Bowman’s capsule

Proximal Tubule - Reabsorption

• Valuable solutes reabsorbed by active or passive transport

• Water follows by osmosis

• Water and solutes leaving the nephron are reabsorbed by nearby blood vessels

Loop of Henle - Reabsorption

• Water reabsorbed, decreasing urine volume

• Salt reabsorbed

• Descending limb of the loop of Henle NOT permeable to salts, VERY permeable to water which results to volume of filtrate to decrease

• Ascending limb of the loop VERY permeable to salts, NOT permeable to water which results to salts maintaining osmolarity of the medulla

Distal Tubule - Regulated reabsorption

• If blood [Na+] is low, the hormone aldosterone is produced

• Aldosterone activates sodium potassium pumps and sodium proton anti-porters in the distal tubule

• Results in Na+ reabsorbed, water follows by osmosis and pH levels regulated

Collecting Duct - Reabsorption

• Filtrate travels through osmolarity gradient again

• Water reabsorbed by osmosis

• Some urea is allowed to leak into the medulla to help maintain osmolarity

Collecting Duct - Regulated reabsorption

• Dehydration triggers the release of ADH (antidiuretic hormone)

• ADH causes cells in the collecting duct to add more aquaporins, retaining water

• Results in water balance achieved, wastes concentrated and osmotic gradient of kidney maintained

Countercurrent flow in nephrons

• Capillaries wrap around the nephron and there are gradients of osmolarity within the nephron

• Blood travels in the opposite direction of the filtrate to efficiently reabsorb water and solutes by diffusion/ osmosis

• Capillary absorbs salt from ascending limb of the loop and capillary absorbs water from descending limb of loop

Digestive system

Purpose is to obtain nutrients from food

Nutrients

Substances that organisms need to survive. Provide energy and building blocks for maintenance/ growth/ reproduction

Food

Any material that contains nutrients. But these nutrients are usually not ready for reabsorption and use by animals

Four main steps for animal digestion

1. Ingestion - get food into body

2. Digestion - break down food to release absorbable nutrients

3. Absorption of nutrients from food

4. Excretion/ Elimination of wastes and undigested materials

The Human Digestive System

• The alimentary canal is one tube

• Food travels in one direction

• Many glands secrete in specific locations to help digest food

• Food digested first, then nutrients absorbed

Mouth

Function: Mechanical and chemical digestion

• Teeth grind and crush foods to increase SA

• Saliva contains water and mucus to lubricate the food and digestive enzymes

Key Enzymes:

• Salivary Amylase: digests starch to release maltose

• Lingual lipase: digests fats to release some fatty acids

Stomach

Function: Mechanical and Chemical digestion

• Stomach muscles contract to churn food into uniform chyme

• In gastric pits

  • Parietal cells secrete HCl, to lower pH as low as 1.5

  • Chief cells secrete pepsinogen, which is activated to pepsin (lower pH)

  • Mucous cells make mucous to protect the stomach from acid/ pepsin

Key Enzyme:

• Pepsin: digests protein into smaller polypeptides

Small Intestine

Function: Chemical digestion and absorption

• Secretions from liver and pancreas neutralize pH, and supply enzymes

Key enzymes:

• Pancreatic Amylase: completes starch digestion to monosaccharides

• Pancreatic Lipase: completes fat digestion releasing fatty acids (with bile salts)

• Proteolytic enzymes: completes protein digestion to amino acids

Key Adaptations:

• Huge surface area: long with folds, villi, and microvilli

• Short distance for nutrient travel: epithelium right next to capillaries

• Lots of transport proteins: allow nutrients to cross cell membranes

Where do nutrients go once absorbed?

Lipids: enter lymphatic system which drains into veins near the heart

All other nutrients: enter liver via hepatic portal vein and adjust their concentrations before circulating.

Large Intestine

Function: Absorption and compaction

• Water is absorbed before excretion/ elimination

• Community of beneficial bacterial symbionts help produce nutrients

Rectum

Function: Absorption of water and holds feces

• Water absorbed before excretion/ elimination

• Feces stored until defecation

Why is a respiratory system necessary?

• Cells need O2 to perform cellular respiration, and need to get rid of CO2

• For most animals, surface area to volume ratio us not sufficient for this gas exchange

Bulk flow/ convection

Movement of fluid molecules as a group; requires extra energy input into the system

Partial Pressure

The contribution of a given gas to the total pressure and tells us how much of a gas is available in a given volume.

• Total pressure of two gasses mixed together is additive

Fick’s Law of Diffusion

Rate of diffusion of high when:

• Area for gas exchange (A) is large

• Distance that the has must travel by diffusion (D) is small

• Partial Pressure Gradient (P2 - P1) is large

Rate of diffusion: k x A x (P2 - P1)/ D

Gas exchange in aquatic animals

Water flows:

• in the mouth

• over gill filaments (composed of many gill lamellae)

• out the operculum (stiff flap of tissue covering the gills)

How do gills maximize efficiency of gas exchange?

• Area for gas exchanged increased by many thin gill filaments

• Thin lamellae walls minimize diffusion distance

• Countercurrent flow of water and blood maintain partial pressure gradients

Gas exchange in terrestrial vertebrates

Air flows:

• Down the trachea

• Into one of 2 bronchi

• Into one of many bronchioles

• Into an alveolus (thin walled sac where gas exchange occurs)

How do lungs maximize efficiency of gas exchange?

• Area for gas exchanged increased by many alveoli

• Thin alveolar walls minimize diffusion distance

• Exhaling pushes out “old” air and inhaling in “new” air to maintain partial pressure gradients

Ventilation in humans

• Negative pressure

• Diaphragm and ribs contract, opening the lungs

• Low pressure in the lungs causes air to rush in

Ventilation in frogs

• Positive pressure

• Air drawn into oral cavity

• With nostrils and mouth closed, oral cavity constricts, pushing air into the lungs

Why don’t humans use countercurrent flow for respiration?

We don’t need it.

• Fish have a different physical environment where ventilation are more difficult.

• Water: low oxygen (relatively low PO2); fluid is dense, harder to move around

• Air: lots of oxygen (relatively high PO2); fluid is light, easier to move around

Gas exchange as homeostasis

• Blood CO2 measured by sensor neurons in the brain

• Integrator compares to setpoint

• If blood CO2 is high, breathing rate increases (effector)

Direction of gas flow in Lungs/ Gills

O2 in , CO2 out

Direction of gas flow in Tissues

O2 out , CO2 in

Moving gases in animals: diffusion

Gases do not dissolve well in liquid

• Bind oxygen to a carrier molecule (hemoglobin)

• Convert CO2 into a chemical that is much more water-soluble (bicarbonate ions)

What is blood

RBC, plasma, WBC, platelets

Explain Strategy 1: Bind oxygen to a carrier molecule

• Hemoglobin protein = 4 polypeptides

• Each polypeptide binds a heme (a small molecule)

• Heme contains an iron ion that can bind one O2 molecule

Explain Strategy 2: Convert CO2 into a chemical that is much more water-soluble

• Carbonic anhydrase in red blood cells catalyzes this reaction

• CO2 is depleted, H+ ions are produced

• Removing CO2 maintains partial pressure - allows more CO2 to diffuse in from tissue

• H+ binds to hemoglobin

How are O & CO2 carried in blood?

O is dissolved in the plasma, in the form of bicarbonate. CO2 binds to hemoglobin

How does hemoglobin bind and release O2 so that it can diffuse in and out of the blood?

• The tissues are actively respiring, using up oxygen, so they have a lower blood pO2

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

• At the tissues, hemoglobin needs to release oxygen into the blood, so that it can diffuse into the cells there, so the cells can use it

Hemoglobin % saturation

Amount of hemoglobin molecules that have oxygen bound to them (40% in tissues, 100% in lungs)

Hemoglobin carries & releases oxygen

• Hemoglobin picks up oxygen when high amounts are present

• Hemoglobin drops off oxygen when low amounts are present

Hemoglobin pH

• It is beneficial for hemoglobin to carry less oxygen at low pH

• Lower hemoglobin saturation = more O2 released to the tissue

• This protein structure is an adaptation that allows a response to the environment at a molecular level

Gas exchange in Alveoli (beginning)

• O2 diffuses into blood due to partial pressure gradient

• Hemoglobin binds O2 with high affinity (high PO2, high pH)

Gas exchange in Tissues

• Hemoglobin binds O2 with low affinity (low PO2, low pH)

• O2 diffuses out of blood die to partial pressure gradient

• CO2 diffuses into blood due to partial pressure gradient

• CO2 converted to bicarbonate (maintains CO2 gradient, lowers pH)

Gas exchange in Alveoli (ending)

• CO2 diffuses out of the blood due to partial pressure gradient

• Bicarbonate and H+ react to reform CO2

2 main types of circulation

Closed & Open

Closed Circulation

Blood flows through connected blood vessels, pumped by muscular hearts. The blood flows through vessels to supply tissues with nutrients

Open circulation

Blood flow through a muscular vessel that act as a pump. Blood empties into an open body cavity to supply the tissues with nutrients, and is returned to the circulation

Pros and Cons of Closed Circulation

Pros: Can generate enough pressure to maintain a high flow rate and can localize blood to tissues that need it most

Cons: Requires more structures (arteries, capillaries, veins) and diffusion is larger (across blood vessel walls and tissues’ cell membrane)

Pros and Cons of Open Circulation

Pros: Hemolymph comes into direct contract with the tissues (small diffusion distance) and fewer blood vessels needed

Cons: Low pressure, so flow rates are usually low, as well and can’t increase flow of hemolymph to specific tissues

Human circulatory systems

Notable features:

• Double circuit - blood pressure in each is independent

• 4 chambered heart

Advantages:

• Blood pumped to tissues (systemic circuit) at high blood pressure, combats gravity

• Blood pumped to lungs (pulmonary circuit) at low blood pressure because these are delicate

• Oxygenated and deoxygenated blood kept separate for efficient gas exchange

Fish circulatory system

Notable features:

• Single circuit - means blood pressure is same throughout

• 2 chambered heart

Advantages:

• Simple (low energy to produce)

• Gravity not a big concern for fish, so low blood pressure to tissue is OK

• Oxygenated and deoxygenated blood kept separate for efficient gas exchange

Frog circulatory system

Notable features:

• Double circuit - partially separated

• 3 chambered heart

• can also perform gas exchange through skin

Advantages:

• Can decrease blood flow to the lungs when under water, increase when breathing air

How does blood move in blood vessels

• Arteries transport blood away from the heart

• Capillaries are small and thin-walled for efficient gas exchange

• Veins transport blood to heart

• From heart → Capillaries → Return to heart

Arteries

• Ventricle contraction propels blood

• Muscle layer in arteries contracts to maintain blood flow between heart beats

Veins

• Skeletal muscle contraction propels blood

• Valves prevent backward flow

The Cardiac Cycle

• Deoxygenated blood enters the right atrium through the vena cava (1)

• Right atrium contracts, pushing blood into right ventricle through tricuspid valve (2)

• Right ventricle contacts, pushing blood into pulmonary artery through pulmonary valve (3)

• Oxygenated blood enters the left atrium (4)

• Left atrium contracts, pushing blood into left ventricle through bicuspid valve (5)

• Left ventricle contracts, pushing blood into aorta through aortic valve (6)

Mammalian Circulatory - Homeostasis

Sensors: Pressure sensors in walls of heart and some arteries measure blood pressure

Integrators: Compares to desired blood pressure

Effectors:

• Cardiac output (volume of blood pumped/ minute)

• Capillary constriction (diverting blood away from less critical areas)

• Vein constriction (decreases overall vein volume)

First line of defence

Preventing pathogen entry

Examples of first line defence

• Many insects have a hard cuticle - includes a layer of wax

• Many soft-bodied invertebrates are covered in mucus

• Human skin covered in a layer of dead cells

Immune system roles

• Detect presence of a pathogen

• Destruction of a pathogen

Innate immunity

• Non-specific immune response

• Always ready (present in broader amounts of animals)

Adaptive immunity

• Only present in vertebrates (mostly)

• Specific for a given invader

Four main classes of mechanisms

• Chemical Defence

• Mechanical Defence

• Behavioural Defence

• Physical Defence

Chemical Defense

A strategy employed by many organisms to avoid consumption by producing toxic or repellent metabolites or chemical warnings

Mechanical Defence

Shedding of skin cells, mucociliary sweeping, shells, spikes, and remove pathogens from potential sites of infection.

Behavioural Defence

Scare off predators using different emotions and flushing actions

Physical Defence

Colour patterns as a advantage to scare off predators like camouflage and warning other of its colour.