Chapter 42 ~ Circulation and Gas Exchange

Circulation system evolution, I

Gastrovascular cavity (cnidarians, flatworms)

Open circulatory •hemolymph (blood & interstitial fluid) •sinuses (spaces surrounding organs)

Closed circulatory : blood confined to vessels

Cardiovascular system •heart (atria/ventricles) •blood vessels (arteries, arterioles, capillary beds, venules, veins) •blood (circulatory fluid)

Circulation system evolution, II

Fish : 2-chambered heart; single circuit of blood flow

Amphibians : 3-chambered heart; 2 circuits of blood flow- pulmocutaneous (lungs and skin); systemic (some mixing)

Mammals : 4-chambered heart; double circulation; complete separation between oxygen-rich and oxygen poor blood

Double circulation

From right ventricle to lungs via pulmonary arteries through semilunar valve (pulmonary circulation)

Capillary beds in lungs to left atrium via pulmonary veins

Left atrium to left ventricle (through atrioventricular valve) to aorta

Aorta to coronary arteries; then systemic circulation

Back to heart via two venae cavae (superior and inferior); right atrium

The mammalian heart

Cardiac cycle : sequence of filling and pumping

Systole - contraction

Diastole - relaxation

Cardiac output : volume of blood per minute

Heart rate - number of beats per minute

Stroke volume - amount of blood pumped with each contraction

Pulse : rhythmic stretching of arteries by heart contraction

Heart Tissue

Contactile tissue: striated, involuntary, branched muscle fibers.

Communication is aided by:

Gap junctions

Intercalated disks

The Heartbeat

Sinoatrial (SA) node (“pacemaker”): sets rate and timing of cardiac contraction by generating electrical signals

Atrioventricular (AV) node: relay point (0.1 second delay) spreading impulse to walls of ventricles

AV bundle (bundle of His) à bundle branches à Purkinje fibers

Electrocardiogram (ECG or EKG)

Blood vessel structural differences

Capillaries •endothelium; basement membrane

Arteries •thick connective tissue; thick smooth muscle; endothelium; basement membrane

Veins •thin connective tissue; thin smooth muscle; endothelium; basement membrane

The lymphatic system

Lymphatic system : system of vessels and lymph nodes, separate from the circulatory system, that returns fluid and protein to blood

Lymph : colorless fluid, derived from interstitial fluid

Lymph nodes : filter lymph and help attack viruses and bacteria

Body defense / immunity

Some plasma flows out of vessel at capillary bed and is returned to circulation via the lymph vessels.

Lymph vessels flow toward heart only and can carry large proteins/lipids that cannot return to circulation in the venule.

Blood

Plasma: liquid matrix of blood in which cells are suspended (90% water)

Hemocytoblast: stem cell for all blood cells (red marrow)

Erythrocytes (RBCs): transport O 2 via hemoglobin, have no organelles in circulation

Leukocytes (WBCs): defense and immunity, only blood “cell” to have a nucleus in circulation

Neutrophils – engulf and kill with chemicals (H 2O 2)

Lymphocytes – immunity; T cells attack infected cells, B cells make antibodies

Monocytes – large cells that become macrophages

Basophils – release histamine (inflammation)

Eosinophils – attack with chemicals (parasites, allergies)

Platelets: cell fragments; clotting

Blood clotting: fibrinogen (inactive)/ fibrin (active); hemophilia; thrombus (clot), embolus (moving clot)

Functions of Blood

Transport: gases, nutrients, wastes, hormones, water (universal solvent)

Protection: clotting, disease defense

Regulation: body temperature, osmotic balance, pH (buffers)

Cardiovascular disease

Cardiovascular disease (>50% of all deaths)

Heart attack - death of cardiac tissue due to coronary blockage

Stroke - death of nervous tissue in brain due to arterial blockage

Atherosclerosis : arterial plaques deposits

Arteriosclerosis : plaque hardening by calcium deposits

Hypertension : high blood pressure

Hypercholesterolemia : LDL, HDL

Gas exchange

CO 2 ß à O 2

Aquatic: •gills •ventilation •countercurrent exchange

Terrestrial: •tracheal systems •lungs

Mammalian respiratory systems

Nasal cavity

Pharynx (upper part of respiratory tract)

Larynx - vocal cords (sound production)

Trachea (windpipe) Bronchi (tube to lungs)

Bronchioles

Alveoli (air sacs)

Diaphragm (breathing muscle)

Breathing

Positive pressure breathing : pushes air into lungs (frog)

Negative pressure breathing : pulls air into lungs (mammals)

Air sacs : birds

Inhalation : diaphragm contraction; Exhalation: diaphragm relaxation

Tidal volume : amount of air inhaled and exhaled with each breath (500ml)

Vital capacity : maximum tidal volume during forced breathing (4L)

Regulation : CO 2 concentration in blood (medulla oblongata)

Respiratory pigments: gas transport

Oxygen transport -

Hemocyanin : found in hemolymph of arthropods and mollusks (Cu)

Hemoglobin : vertebrates (Fe)

Carbon dioxide transport -

Blood plasma (7%)

Hemoglobin (23%)

Bicarbonate ions (70%)

CO 2 + H 2O ß à H 2CO 3 ß à H + + HCO3 -

Deep-diving air-breathers -

Myoglobin : oxygen storing protein