gen bio 2 - lecture 23: circulation

circulatory system overview + LIST two types

organisms with circulatory systems have 3 components: fluid, vessels, heart

2 types:

• open circulatory system

• closed circulatory system

open circulatory system

• fluid = hemolymph = interstitial fluid

• heart contractions: hemolymph → vessels → interconnected sinuses

• heart relaxations: draw hemolymph back into heart

low pressure, low energy, low efficiency

closed circulatory system

• blood: circulatory fluid confined to vessels

  • heart = pumps blood through branched vessels

  • exchange happens @ capillaries

high pressure, more efficient, requires more energy

VERTEBRATES

fish vs amphibian vs mammals/birds circulation and circuits

FISH

• single circulation

• heart has 2 chambers

  • 1 atrium and 1 ventricle

AMPHIBIAN

• double circulation

• heart has 3 chambers

  • 2 atria and 1 ventricle

• blood flow in 2 circuits:

  • pulmocutaneous circuit: lungs and skin take up oxygen

  • systemic circuit: delivers oxygen

    • some mixing occurs between the two

MAMMALS/BIRDS

• double circulation

• heart has 4 chambers

  • 2 atria and 2 ventricles

• blood flow in 2 circuits:

  • pulmonary and systemic - NO MIXING OCCURS

OVERALL:

1. right atrium (receives deoxygenated blood)

2. right ventricle (pumps blood to lungs)

3. pulmonary artery (splits into 2)

4. capillaries of right and left lung (gas exchange)

5. pulmonary vein (merges again; returns oxygenated blood)

6. left atrium (receives oxygenated blood)

7. left ventricle (pumps blood to body)

8. aorta

9. capillaries of body

• right side of heart = deoxygenated blood going TO lungs

• left side of heart = oxygenated blood going to body

structure of human heart (include atria/ventricles, and 4 valves)

heart: pumping organ with 2+ muscular chambers

atria: receive blood from veins

ventricles: pump blood to arteries

4 valves (flaps of connective tissue that prevent backflow):

• 2 atrioventricular (R and L AV) valves between atria and ventricles

  • blood from tissues to atria

  • blood pressure in atria opens AV valves

  • ventricular contractions close AV valves

• 2 similunar valves from ventricles to arteries

  • pulmonary valve: right ventricle to pulmonary artery

  • aortic valve: left ventricle to aorta

heart contraction/heartbeat OVERVIEW

• auto-rhythmic, internal initiation (no action potential needed)

• sinoatrial node: pacemaker of heart (small mass of cardiac muscle in R atria)

process of heartbeat (8 steps)

1. sinoatrial node generates action potential within cardiac muscle

triggered by leaky calcium channels!!

2. impulse from sinoatrial node spreads through atria

3. atria contract simultaneously

4. action potential reaches atrioventricular node (auto-rhythmic cells in septum between RA and RV)

5. 1/10th second delay @ AV node

allows atria to complete contraction before ventricles start

6. action potential transmitted via bundle branches and AV node to heart apex

7. spreads through purkinje fibers throughout ventricles

8. ventricles contract

regulation of heart rate (by nervous system vs by endocrine system)

NERVOUS SYSTEM:

• baroreceptors: sensory receptors in wall of blood vessels and heart

1. detect change in blood pressure

2. cardiac centers in medulla oblongata

3. autonomic nerves

4. SA node

sympathetic: increases heart rate and blood pressure

parasympathetic: decreases heart rate and blood pressure

ENDOCRINE SYSMEM:

• stress: adrenal medulla → epinephrine released → increased heart rate

• temp: higher temp → faster heart rate

blood vessel structure

3 layers:

1. endothelium: lines lumen, smooth

2. smooth muscle: thicker in arteries and thin in veins

3. connective tissue: many elastic, collagen fibers

arteries vs capillaries vs veins

ARTERIES

carry blood from heart to organs, muscles, etc

arteries → arterioles → capillaries

VEINS

carry blood from organs to heart (found between skeletal muscle)

capillaries → venules → veins

**veins and arteries differ in DIRECTION of blood flow and NOT OXYGEN CONTENT

CAPILLARIES

microscopic blood vessels found in all tissues

ONLY LOCATION OF EXCHANGE BTWN BLOOD AND INTERSTITIAL FLUID

• at least one capillary near every cell in body

• 2 layers: endothelium + basal lamina (thin walls)

mechanism of exchange (include interstitial fluid)

• thin capillary lining allows for DIFFUSION of nutrients, ions, gasses, and waste

  • under pressure, some plasma leaves capillaries = INTERSTITIAL FLUID

interstitial fluid: fluid directly surrounding all tissues, has NO RED BLOOD CELLS

• hypotonic relative to blood

• blood pressure and osmotic imbalance (antagonistic forces) lead to fluid exchange!!!

  • arterial end of capillaries = net fluid out

  • venous end of capillaries = net fluid in

not all lost fluid returns!! about 15% remains interstitial fluid

lymphatic system (functions and anatomy)

functions:

• returns extra interstitial fluid to blood

• absorbs lipids from small intestine

• defends against disease

anatomy:

• contains lymph (watery fluid derived from interstitial fluid)

• travels through lymph vessels

  • lymph nodes: where vessels meet

  • return to blood vessels via lymph ducts

  • flows due to muscle contractions