10-1: Circulation

Question 1

Components of all circulatory systems

Answer 1

-Circulatory systems link exchange surfaces with cells
throughout the body.
-All circulatory systems have the following 3 components:
• A circulatory fluid (blood or hemolymph)
• A set of tubes (vessels)
• A muscular pump (heart)
- Hemolymph is the fluid found in arthropods and mollusks.

Question 2

Types of circulatory systems: open system

Answer 2

-Hemolymph is the circulatory fluid in the open systems =
the interstitial fluid that bathes body cells.
-Chemical exchange occurs between the hemolymph and
cells.
-An animal with an open circulatory system has 1 or more hearts. The heart is the dorsal vessel that has chambers separated by valves called ostia, which ensure 1-way flow. When these hearts contract, they
force the hemolymph to travel out of the vessels into the space in the body called hemocoel. When the hearts relax, hemolymph is drawn back into them through ostia.

Question 3

Types of circulatory systems: closed system

Answer 3

-Blood is the circulatory fluid in
the closed systems = distinct
from the interstitial fluid that
bathes body cells.
-Chemical exchange occurs between the blood and the interstitial fluid, and then between the interstitial
fluid and body cells.
-In a closed circulatory system blood is confined to vessels and is separate from the interstitial fluid,
which is everywhere else inside our body. There may also be 1 or more hearts present.
• Closed systems are more efficient at transporting circulatory fluids to tissues and cells. It also allows
more rapid blood flow; more efficient transport of wastes and nutrients, and higher blood pressure than is possible in open circulatory systems.

Question 4

no circulatory system

Answer 4

• Simple animals, such as cnidarians (hydra) have a body wall only two cells thick that encloses a gastrovascular cavity. The gastrovascular cavity functions in both digestion and distribution of substances throughout the body. These animals do not have a need for a circulatory system.

Question 5

single circulation

Answer 5

• the system where the blood passes through the heart once in each complete circuit (fish).
• Single circulation works great in water, but when animals move onto land, they loose quite a bit of that pressure as the blood goes to the – now lungs, so this system is not efficient on land. That is why on land, animals have evolved a 2-loop system and either a 3- (amphibians) or a 4-chambered heart (birds and mammals).

Question 6

double circulation

Answer 6

1) there is one circuit that goes from the heart to the lungs, called pulmocutaneous circuit in amphibians – because it goes
to the lungs (‘pulmo’) but also to the skin, since amphibians breathe through the skin (’cutaneous’) as well; and called
pulmonary circuit in birds and mammals – the one that goes to the lungs; and
2) there is the second circuit that goes from the heart to the rest of the body, called systemic circuit.
3) THIS ALLOWS FOR OXYGENATED AND DEOXYGENATED BLOOD TO NOT MIX IN THE HEARTS OF BIRDS AND MAMMALS.
• In amphibians, there is some mixing of the oxygen-rich and oxygen-poor blood in the area of the heart. This is not very
efficient for other animals, so birds and mammals have a complete separation between the ventricles. Their metabolic
requirements are much higher, and having the hearts completely divided into 2 atria and 2 ventricles, prevents mixing of the blood in the heart (more efficient).

Question 7

Blood vessels

Answer 7

-arteries, veins, capillaries
-• All blood vessels are built of similar tissues, and they all have three similar
layers:
1. A layer of connective tissue with elastic fibers that allow the vessel to stretch and
recoil.
2. A middle layer of smooth muscle and more elastic fibers.
3. An endothelium – a single layer of simple squamous epithelium that provides a smooth surface for the blood flow.

Question 8

capillaries

Answer 8

-have only the endothelium and its basement membrane (this facilitates the exchange of substances between the blood and the interstitial fluid
that bathes the cells). They lack two outer layers.

Question 9

arteries

Answer 9

-have thicker middle and outer layers than veins – blood is pumped at high
pressure by the heart. They have an extra layer of elastic tissue (to help stretch the artery walls).
-High blood pressure (you can feel pulse)
• Thick-walled (more muscular and elastic)
• Blood flows away from heart
• Most (except pulmonary) contain oxygenated blood
• Blood moves in one direction due to high blood pressure and
smooth muscle contraction

Question 10

veins

Answer 10

• thinner walls
  – they carry blood back to the heart at lower pressure than arteries. Veins have valves inside to prevent the back-flow of the blood.
  Low blood pressure (you can’t feel pulse)
  • Thin-walled compared to artery of similar size
  • Blood flows to heart
  • Most (except pulmonary) contain deoxygenated blood
  • Blood moves in one direction due to one-way valves, skeletal muscle contraction and smooth muscle contraction.

Question 11

Major arteries

Answer 11

• aorta
• coronary arteries
• carotid arteries
• pulmonary artery

Question 12

aorta (aortic arch)

Answer 12

carries blood immediately leaving the heart (more specifically, leaving the left ventricle)

Question 13

coronary artery

Answer 13

several smaller arteries branch off from the aorta, and supply blood to the heart itself

Question 14

carotid arteries

Answer 14

supplies blood to head

Question 15

pulmonary arteries

Answer 15

supplies blood to lungs
(note that blood in pulmonary arteries is DEOXYGENATED, as
blood moves to lungs to get oxygenated)

Question 16

major veins

Answer 16

• Jugular veins: carries blood from head to heart
• Subclavian and brachial veins: carry blood away from arms to
heart
• Both jugular and subclavian veins lead into the superior (anterior) vena cava, which brings blood to right atrium of
heart.
• Blood from lower body leads into the inferior (posterior) vena cava, which also brings blood to right atrium of heart.
• Pulmonary veins: bring blood to left atrium of heart after leaving lungs (note that blood in pulmonary veins is OXYGENATED)

Question 17

functions of blood

Answer 17

• carries O2 and CO2
• transports nutrients
• moves wastes
• conveys hormones
• delivers immune cells to sites of infection
• delivers platelets
• distributes heat

Question 18

summary

Answer 18

• RIGHT side = deoxygenated blood
from body pumped to lungs
• LUNGS = gas exchange • LEFT side = oxygenated blood
from lungs pumped to body

Question 19

contractions of heart

Answer 19

• Systole = the contraction of the atria and the ventricles
• Diastole = relaxation of the atria and the ventricles
• The sequence of this contraction is called the cardiac cycle = 1 diastole and 1 systole for both atria and ventricles.
• Atria contract slightly before the ventricles.
Ventricles -> pulmonary artery (from right ventricle) and ->
the aorta (from left ventricle).
• Blood pressure measured in the systemic arterial circulation
at the peak of ventricular ejection into the aorta is the
systolic blood pressure.
• Blood pressure measured just prior to ventricular ejection is
the diastolic blood pressure

Question 20

contractions of heart (2)

Answer 20

• Electrical signals -> contractions of the heart muscle
• Pacemaker cells (located in the right atrium and called the
sinoatrial node) initiate the cardiac contraction in vertebrates
• Signals from the nervous system and the endocrine system regulate the heart rate and the strengths of ventricular
contractions.
• The contraction generated by the sinoatrial node, rapidly
spreads throughout the right and the left atria.
• An electrocardiogram (ECG) = a recording of the electrical
events that occur over the course of the cardiac cycle

Question 21

heart cycle

Answer 21

MOMENT D:
• Both ventricles are relaxed and
expanding - setting up a negative pressure in the ventricles. As a result, blood flows from veins into atria and into ventricles.
• The atrioventricular valves
(between each atrium and
ventricle) are open.
• The semilunar valves (one
between the left ventricle and
the aorta, and another between
the right ventricle and the
pulmonary artery) are closed,
keeping the blood from coming
back from the aorta and
pulmonary artery