Download Chapter 32 Circulation

Circulation
Chapter 32
Circulatory System Basics
• Three major parts
– Blood
– Blood vessels
– Heart
Two Types of Systems
• Open circulatory system: space within
the body cavity (hemocoel)
– Found in arthropods and most mollusks
– Circulates hemolymph
– Similar to interstitial fluids
– Used to transport nutrients, wastes,
hormones, rarely used for O2
Two Types of Systems
• Closed circulatory system: blood
confined within continuous vascular
network with a pumping heart
– Found in some invertebrates and all
vertebrates
Diverse Functions
1. Transport of O2 and CO2
2. Distribution of nutrients
3. Transport of waste
4. Distribution of hormones
5. Regulation of body temperature
6. Prevent blood loss
6. Protect against disease
Evolution of the Vertebrate Heart
• Vertebrate hearts have muscular
chambers called atria and ventricles
• Can have 2, 3, or 4 chambers
– Atria collect blood from body
• Contract and deposit blood in ventricles
– Ventricles contract and discharge blood to
body
Evolution of the Vertebrate Heart
• Two chambered hearts
– Earliest vertebrate hearts with one atrium
and one ventricle
– Example: fish hearts
– Conus arteriosus (aorta) carries blood away
from ventricle
– Sinus venosus – carries blood to the atrium
Evolution of the Vertebrate Heart
• Three chambered hearts
– Have two atria and one ventricle
– Examples: amphibian and most reptile
hearts
– Double circulation – blood moves thru heart
twice while completing a circuit. Systemic &
pulmonary circulation
– No separation of right & left sides (mixing of
oxygenated & deoxygenated blood)
Evolution of the Vertebrate Heart
• Four chambered hearts
– Most advanced
– Have two atria and two ventricles
– Separation of O2-rich and O2-poor blood
maximizes O2 levels in blood
– Examples: bird and mammal hearts
Human Heart Function
• Two types of blood vessels connect to
heart chambers:
– Veins: carry blood to atria
– Arteries: carry blood away from ventricles
Human Heart Function
• Made of two separate pumps
– Right pump: made of right atrium and right
ventricle
– Left pump: made of left atrium and left
ventricle
– Right atrium receives O2-poor blood from
body by superior and inferior vena cavae
– Right ventricle ejects O2-poor blood into
pulmonary arteries to be oxygenated by
lungs
Human Heart Function
– Left atrium receives O2-rich blood from lungs
by pulmonary veins
– Left ventricle ejects O2-rich blood into aorta to
be distributed to body tissues
– Pumps separated by ventricular septum
Heart Valves
• Heart valves insure one-way flow of blood
through heart
– Insures that O2-poor blood is sent to lungs
and O2-rich blood is sent to body tissues
– Atrioventricular valves: allow blood to flow
from atria to ventricles, prevent back flow
– Semilunar valves: allow blood to flow from
ventricles to arteries, prevent back flow
Cardiac Muscle
• The heart is composed of cardiac muscle tissue
• Cardiac muscle cells are
– Small, branched, and striated
– Linked to one another via intercalated discs
containing gap junctions
– Gap junctions allow the electrical signals that trigger
contractions to spread directly and rapidly from one
muscle cell to the next
• This results in the coordinated, synchronous
contraction of heart muscle
The Cardiac Cycle
• The heart beats in a coordinated fashion:
– Both atria contract and pump blood into
ventricles
– Both ventricles contract and pump blood into
arteries
– All chambers relax briefly before the cycle
repeats
– This cardiac cycle lasts less than 1 second
Blood Pressure
• Heart chamber contractions generate
blood pressure that drives blood flow:
– Systolic pressure: blood pressure during
ventricular contraction
– Diastolic pressure: blood pressure during
ventricular relaxation
– Pulse – expansion & contraction of artery
walls during heartbeat
High Blood Pressure
• High blood pressure (hypertension) is caused
by the constriction of arterioles
• Causes resistance to blood flow and strain on
the heart
• Borderline reading for high blood pressure is
140/90
• Hypertension interacting with hardened arteries
can lead to blood clot formation
• Blood clots can block arteries, leading to
– Heart attack
– Stroke
Coordination of Contractions
• Pacemaker cells coordinate cardiac cycle
– Heart cells that regularly produce spontaneous
electrical impulses
– Impulses spread throughout heart muscle cells and
stimulate them to contract
• Sinoatrial (SA) node is the primary pacemaker
– In upper wall of right atrium
– Generates impulses that spread throughout cardiac
muscle cells of atria
– Atrial cells contract in unison and finish emptying
blood
Coordination of Contractions
• Atrioventricular (AV) node: second
pacemaker cell cluster
– In floor of right atrium
– Stimulated by SA node impulse
– After a 0.1 second delay, sends impulse to
ventricles by excitable fibers
– Ventricles contract when stimulated
Control of Heart Rate
• SA node maintains heart rate of 100 beats per
minute (bpm)
• Nervous system modifies heart rate:
– At rest, parasympathetic nervous system slows
heart rate to ~70 bpm
– During exercise and stress, sympathetic nervous
system increases heart rate
• Endocrine system modifies heart rate
– Under stress, the hormone epinephrine is released
– Stimulates SA node and increases heart rate
Two Major Blood Components
• Plasma: fluid portion of blood
– 55-60% of blood volume
• Cellular components: made of red blood cells, white
blood cells, and platelets
– 40-45% of blood volume
• Plasma
– ~90% water
• Other components
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–
–
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Hormones
Nutrients
Gases
Salts
Wastes
Proteins
Plasma Proteins
• Three major types
– Albumins: maintain osmotic pressure of
blood
– Globulins: transport nutrients and act in
immunity
– Fibrinogen: involved with blood clotting
Red Blood Cells
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•
•
•
Also called erythrocytes
Make up 99% of all blood cells
Carry oxygen from lungs to tissues
Human erythrocytes have a biconcave disk
shape
• Red color caused by pigment hemoglobin
– Composed of four polypeptide chains and four ironcontaining heme groups
– Each heme group binds to O2 in lung and turns
hemoglobin cherry red
– Hemoglobin releases O2 and picks up some CO2 at
tissues
Red Blood Cell Life Span
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•
•
•
Formed in red bone marrow
During formation, nucleus is removed
Red blood cells live ~ 4 months
2 million red blood cells die per second
and are replaced by bone marrow
– Removed by liver and spleen
– Iron recycled and used to form more
hemoglobin
Red Blood Cell Life Span
• When blood O2 levels are low,
erythropoietin is released by kidneys
– Stimulates additional red blood cell formation
by bone marrow
– Controlled by negative feedback
White Blood Cells
• Also called leukocytes
• Make up < 1% of all blood cells
• Most protect body against disease
Example: lymphocytes
– Can produce antibodies used in immunity
• Example: macrophages
– Mobile and amoeba-like
– Engulf foreign particles and bacteria
Platelets
• Fragments of megakaryocytes formed in
the red bone marrow
– Pieces pinched off and enter circulation
• Called thrombocytes
• Involved in clotting
• Last 10-12 days
Blood Clotting
• Keeps animals from bleeding to death
• Blood clot
– Formed from sticky fibrin protein threads,
platelets, and other cells forming patch over
wound site
• Results from interaction among circulating
plasma proteins, particularly thrombin
and fibrinogen
Blood Clot Formation
• Aggregated platelets in clot constrict after
~ 30 minutes
– Tightens fibrin web and forces liquid out of
clot
– Results in denser, tougher clot
• On skin surface, called a scab
Pattern of Blood Flow
• Blood flows through blood vessels
• From heart 
Arteries  arterioles  capillaries  venules 
veins  back to heart
Arteries
• Thick walled vessels
– Contain smooth muscle and elastic tissue
to withstand high pressure
• Elastic recoil maintains blood pressure
during diastole
• Carry oxygenated blood (except
pulmonary arteries)
Arterioles
• Branch off of arteries
• Smaller in diameter
• Help control distribution of blood flow
Capillaries
• Tiniest vessels—thin, single-cell thick for easy
diffusion
• Allow exchange of materials between blood,
interstitial fluids, and body cells
– Nutrients
– Gases
– Hormones
• Blood pressure drives fluid leakage out of
capillaries and into spaces surrounding tissue
cells (i.e., interstitial fluid)
Venules
• Capillaries merge to form larger venules
• Venules merge to form veins
Veins
• Contain smooth muscle and elastic
tissue
– Wider, thinner walled than arteries
– Contain one-way valves that allow blood to
flow only to heart
– Skeletal muscle contractions compress
veins and drive blood movement towards
heart
Distribution of Blood Flow
• Muscular arteriole walls contract and relax
to redirect blood flow and regulate blood
pressure
• Controlled by nerves, hormones, and
nearby chemicals
The Lymphatic System
• Includes lymphatic vessels, lymphatic
capillaries, lymph nodes, thymus, and
spleen
• Functions
– (1) Returns excess interstitial fluid to
bloodstream
– (2) Transports fats from small intestine to
bloodstream
– (3) Contributes to immunity
Lymphatic Capillaries
• “Dead-end” lymphatic capillaries collect
excess interstitial fluid from tissues
– Lymph: fluid in lymphatic system
• Lymphatic capillary cells overlap
– Act as one-way valves
– Allow fluid and particles to drain into lymphatic
capillaries
– Merge to form lymphatic vessels
Lymphatic Vessels
• Similar in structure to veins, including oneway valves
• Muscle contractions drive lymph flow
Return of Fluid to the Blood
• 3 to 4 liters of excess interstitial fluid are
generated per day
– Collected by lymphatic system and deposited
into general circulation where thoracic duct
joins with vena cava
• Elephantiasis: a disease caused when
parasitic roundworms colonizes lymphatic
vessels
– Prevent draining of lymph and causes
extreme swelling (edema)
Transport of Dietary Fats
• Small intestine has many lymphatic
capillaries
• Lymph is composed of ~1% of fattransporting particles
– Too large to diffuse into blood capillaries
– Travel in lymph until introduced into general
circulation
Defense Against Disease
• Tonsils: patches of connective tissue
containing many lymphocytes
– Destroy bacteria and viruses
• Lymph nodes: kidney-shaped structures
found connecting lymph vessels
– Contain many macrophages and lymphocytes
– Destroy foreign particles in lymph
Defense Against Disease
• Thymus: found above heart
– Important site of lymphocyte development
• Spleen: found in abdominal cavity
– Functionally similar to a lymph node, but filters
blood instead of lymph
– Destroys old red blood cells