Chapter 42: Circulation &Gas Exchange

Circulatory & Phylogeny

• Diffusion is inefficient over distances more than a few mm.

• Circulatory system ensures that no substance must diffuse very far and connects the aqueous environment of cells to organs that exchange gases, absorb nutrients, and dispose of wastes

• Those that lack a circulatory system utilize a gastrovascular cavity to digest and distribute substances throughout body

Ex: hydra, jellyfish, planarians

Open vs. Closed• Two types of circulatory systems:

*both utilize fluid (blood), set of tubes (vessels or sinuses), and pump (heart)

1. Open system – no distinction between blood and interstitial fluid

- hemolymph is pumped through sinuses to reach organs and parts of body

2. Closed system – blood is confined to vessels and separate from interstitial fluid

- materials are exchanged by diffusion between vessels and fluid

- higher blood pressure is more effective at transport of fluids to meet metabolic demands

Open vs. Closed

Cardiovascular System

• Most vertebrates have muscular heart with 1 or 2 atria, and 1 or 2 ventricles

- always pumps atrium to ventricle• 3 blood vessels of transport of blood, nutrients,

and wastes1. Arteries – carry blood away from heart2. Veins – carry blood toward heart3. Capillaries – exchange blood and gases

between veins and arteries

Vertebrate Circulation

Vertebrate Circulation

Fish - 2 chambers atrium and ventricle - gill capillaries pick up oxygen send it to systemic capillaries - return to heartAmphibians - 3 chambered heart 2 atria, 1 ventricle- pulmocutaneous circuit moves to lungs for oxygen- returns to heart; oxygen rich blood pumped from heart

to systemic circuit

Vertebrate Circulation

Reptiles ( true double circulation)- 3 chambered heart; 2 atria, 1 ventricle with partially divided

septum (less mixing of blood)- Separate pulmonary loop to lungs for oxygen; cycle back to

heart and pump to systemic loop and back to heart Mammals and Birds- 4 chambered heart; 2 atria, 2 ventricles- Right side separation of pulmonary loop to lungs for oxygen;

back to left side of heart where ventricle pumps to systemic loop

- Atrial valves to prevent backflow

Pathway of Circulation1. De-oxygenated blood enters right side of the heart from both superior

(anterior) and inferior (posterior) vena cava.2. Blood moves from right atrium through the atrioventricular valve to the

right ventricle3. From the right ventricle blood exit the heart in the pulmonary artery to

the lungs4. Gas exchange in the lungs allows oxygenated blood to circulate back to

the heart through the pulmonary vein.5. Oxygenated blood enters left side of the heart into the left atrium.

Blood flows through atrioventricular valve to the left ventricle6. Aorta (largest artery) carries blood from the ventricle first to the

coronary arteries that give blood to heart muscle, then to other organ systems throughout the body.

7. Deoxygenated blood is cycled back to the heart by way of Superior and inferior vena cava

Mammalian Heart

Mammalian Heart

• Cardiac cycle refers to the rhythmic cycle of contracting and relaxing or pumping and refilling blood

systole – contraction of heart moving blood out of ventricle

diastole – relax and refill of blood into the ventricle

Mammalian Heart

• Cardiac output – volume of blood per minute that the left ventricle pumps to system loop

• CO depends on heart rate ( beats per min.) and stroke volume

• Stroke volume – amount of blood pumped by ventricle with each contraction

• Pulse – stretching of arteries by pressure of blood pumped by contraction of ventricles

Mammalian Heart

• Valves – flaps of connective tissue that prevent backflow and circulate blood in correct direction

- 2 atrioventricular - 2 semilunar between left ventricle and

aorta, and pulmonary artery and right ventricle• Heart murmur – condition caused by defect in

one or more valves – hissing sound as blood squirts backward

Heart’s Rhythmic Beat

• Sinoatrial node (SA node) or pacemaker – sets the rate and timing of cardiac muscle contraction

- located in wall of right atrium where superior vena cava enters heart

- generates electrical impulses like nerve cells causing atria to contract in unison

• Atrioventricular node – main relay point between right atrium and ventricle

• Electrocardiogram (ECG) – record of electrical impulses that travel through the cardiac muscle during the heart cycle

Heart’s Rhythm

• SA node sets tempo, but is influenced by the following factors:

1. nerves that speed up and slow down pacemaker2. Hormones – example epinephrine3. Body temperature4. Activity level

Principles of Circulation

• Same physical principles that govern a plumbing system influence functioning of animal circulatory system

• Infrastructure is network of blood vessels of varying size, speed, and pressures

• Law of continuity- fluid movement through pipes will increase speed if the diameter of the pipe decreases in order to maintain a constant flow rate.

Blood Pressure

• Blood pressure – hydrostatic pressure of blood against the wall of a vessel and that propels blood

- arteries have higher pressure that other blood vessels because of smaller thick walls

• Peripheral resistance is created by the impedance of arterioles from relieving pressure of blood entering the arteries with each contraction

Lymphatic System• Large accumulations of fluids and blood proteins can

be lost each day flowing through capillaries• Lymphatic system returns lost fluid and proteins

(lymph) to the blood that intermingles with cardio system

- maintains volume and protein concentration of blood

• Lymph vessels have valves to prevent backflow and rhythmic contractions move fluid toward the heart

• Lymphatic system also helps defend against infection (lymph nodes contain large clusters of WBCs)

Blood Composition• Blood consists of several kinds of cells suspended in

plasma- plasma is 90% water- solvent for transport- ions like Na, K, Mg, & Cl help regulate

membrane permeability- proteins like Albumin along with ions help

maintain osmotic balance and act as pH buffers- Fibrinogen is a protein clotting factor- Immunoglobulins serve as defense proteins against viruses or foreign agents

Blood Composition• Cellular elements of blood

1. Red blood cells – transport oxygen with iron containing protein hemoglobin

- most numerous blood cell2. White blood cells (leukocytes) – defense against

infections- monocytes, neutrophils engulf bacteria and debris- lymphocytes develop into B cells and T cells

3. Platelets – clotting factors that originate from pinched off cytoplasmic fragments

- sealant is inactive form fibrinogen which is converted to fibrin to create clot

- clotting factors begin cascade of reactions to convert to fibrin

Blood Clotting

Stem Cells

• Cellular elements of blood wear out and are replaced constantly

• All cellular elements develop from a common source – stem cells

- located in marrow of ribs, pelvis, vertebrae and breastbone

- termed as pluripotent meaning all have potential to develop into any kind of blood cell or platelet

Cardiovascular Disease

• Disease is result of disorders of the heart and blood vessels

Cholesterol – LDL and HDL• Artherosclerosis – disease caused from plaques narrowing

the bore of the artery• Hypertension – high blood pressure can be caused from

atherosclerosis which narrows and reduces elasticity of vessels

• Heart attack – death of cardiac muscle from prolonged blockage of coronary arteries

• Stroke – death of nervous tissue in the brain

Gas Exchange• Gas exchange – uptake of

molecular O2 from environment and discharge of CO2 to outside

• Respiratory medium is the source of oxygen

• Respiratory surface is part of body where gases are exchanged - diffusion

Respiratory SystemsPathway of air flow:

1. Air enters the nostrils where hairs filter, warmed, humidified, and sampled for odors

2. Nasal cavity leads to pharynx- division between esophagus and trachea

3. Air moves past glottis into the trachea4. Trachea forks into branches called bronchi5. Bronchi divide into finer tubes called bronchioles

(within the lungs)6. At the tips of the bronchioles are the tiny grape- like

clusters called alveoli- location of gas exchange across capillary

walls

Respiratory System

Breathing• Mammals ventilate lungs by negative pressure breathing

- pulling air into the lungs instead of pushing- diaphragm – skeletal muscle at the bottom wall of chest cavity

- contracts moving down to drawn air in (inhalation)and expand rib cage (pulling it up)

- relaxes moving up to push CO2 out (exhalation)

• Tidal volume – the volume of air a mammal inhales and exhales with each breath

Breathing

Control Centers of Breathing

• Main breathing control centers are 2 regions of the brain stem called the pons and medulla oblongata

- set the basic rhythm- negative feedback mechanisms are used to regulate breathing activity between lungs and medulla