HSCI100 – Spring2014
An Outline and Synopsis of Concepts
For Exam II
The Cardiovascular System
In the cardiovascular system, the heart pumps the blood, and the blood vessels transport
blood around the body. Molecule exchanges at capillaries refresh the blood and the
tissue fluid (interstitial fluid) as it moves nutrients, wastes, gases, blood cells and more.
Blood vessels ensure constant delivery
Blood vessels generally have 3 layers of tissue: an inner endothelium, a smooth muscle
layer, and an outer connective tissue layer. Arteries, which branch into smaller arterioles,
take blood away from the heart to capillaries. Arteries have thick vessel walls and have
high blood pressure. Capillaries are single cell layer thick and carry out exchange with
tissue. Flow to capillary beds can be regulated by sphincter muscles and shunt pathways.
At tissue capillaries, nutrients and oxygen are exchanged for carbon dioxide and other
wastes. The relatively high hydrostatic pressure at the arterial end of the capillary beds
forces fluid out into tissues, while at the venous end of the capillary bed, the higher
osmotic (colloid oncotic) pressure helps to retrieve fluid back into the vasculature. In this
way, tissue fluid and the body’s cells remain replenished. Leading away from the
capillaries, venules join to form veins that take blood back to the heart. Veins hold more
blood than arteries, but have little blood pressure, thinner vessel walls (less smooth
muscle and connective tissue layers) and one way valves to help blood move back to the
heart. The vessels and one way valves of the lymphatic system also help to retrieve
interstitial fluid from tissues and return it back to the heart. Moving skeletal muscle also
serves to push blood back to heart via the veins and fluid via the lymph vessels.
The heart is a pump
The right side of the heart pumps blood to the lungs (pulmonary circuit), and the left side
of the heart pumps blood to the rest of the body: systemic circuit. Branching off the aorta
are the coronary arteries that supply what might be considered the third circuit: the
‘coronary circuit’. Atria (upper chambers) contract first, pushing blood through
atrioventricular valves into the ventricles (lower chambers). The ventricles contract next
and send blood out through semilunar valves to the lungs (right ventricle, and pulmonary
valve) or the rest of the body (left ventricle and aortic valve). The left ventricle has
thickest/strongest cardiac muscle and the aorta is the biggest artery.
Systole refers to the contraction phase of the heart and diastole refers to the relaxation
phase. The pressure levels seen in systole and diastole are common measures of heart
health and a common target is 120/80 mm Hg for systole/diastole readings. The heart
beat is very regular and is controlled by a pacemaker center: the sinoatrial node, which
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triggers contraction of the atria and the signal is next relayed via the atrioventricular node
and atrioventricular bundle to the ventricles so they contract a short time after the atria.
The rate can also be controlled by the medulla oblongata in the central nervous system.
Neurotransmitters and hormones, like epinephrine (aka adrenaline) and acetylcholine
speed up or slow down the heart rate, respectively. The rate is measured as your pulse.
Heart disease is a common cause of illness and death
Hypertension (high blood pressure) and atherosclerosis (hardening of the vessels) are two
cardiovascular disorders that can lead to stroke, heart attack, aneurysm, and
hemorrhaging. The major problem with these disorders is the lack of blood supply and
death of tissues, organs and ultimately the person if the damage is severe enough.
Irregular heart beat is termed arrhythmia or fibrillation. A number of interventions are
available and frequently implemented in CVD, not the least of which is modification of
diet, environment, and exercise.
Blood is a liquid connective tissue
Blood is the major transporter of the body. It fights infections and helps regulate body
temperature and the pH of body fluids and your tissues. Blood cells are born in the red
bone marrow (spongy bone regions).
Red blood cells transport oxygen
Mature red blood cells (RBC) lack nuclei and contain mostly hemoglobin, which is
composed of 4 globin polypeptides (α2β2) each carrying a heme group containing iron
(Fe) that binds oxygen. Hemoglobin transports oxygen (4 O /hemog2obin) and helps
transport carbon dioxide, CO . 2O is 2lso transported by dissolving as bicarbonate ion,
HCO , in the blood plasma, and serves as an important buffer to regulate body pH.
RBC production is regulated by the hormone erythropoietin, which is made by the
kidneys. A low level of RBC is called anemia and misshapen RBC (resulting from
mutant hemoglobin proteins) that do not survive as long as normal RBC and block
capillaries are found in sickle cell anemia.
White blood cells defend against foreign invaders and cancer
White blood cells (WBC) collectively fight infections. Neutrophils are the most common
WBC and carry out phagocytosis. Eosinophils are important in fighting parasitic worms
and have a role in allergic reactions. Basophils and mast cells release histamine in
response to pathogens, which helps to trigger the inflammatory response. Monocytes
develop into macrophages, which are professional phagocytic cells. Lymphocytes
develop into T- and B-cell types and they are the second most common WBC type.
[Additional information on WBC is found below in the Lymphatic and Immune System
Platelets are essential to blood clotting or coagulation.
Platelets are fragments of megakaryocytes that clump together and seal breaks in a blood
vessel (hemorrhage) and prevent loss of blood. The clotting reaction is a cascade of
protein activation and cleavage steps that results in a net of fibrin (made from the
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fibrinogen precursor) that traps red blood cells. The process of platelet activation and
triggering of the protein clotting cascade (sometimes called thrombosis) are both positive
feedback cycles. Hemophilia is a disease resulting from deficient blood clotting and a
clot (thrombus) that moves and interrupts normal blood flow is an embolus.
Blood typing and transfusions
Before a blood donation can be given, it must be typed because only certain type(s) of
blood are compatible. This is based upon antibody recognition of ABO blood group
antigens that decorate RBC. Other antigens, e.g. Rh factor, can also play a role in blood
compatibility. O-type RBC lacks any antigens so it can be tolerated by anyone and is
thus called the universal donor blood type. People with AB blood type do not carry
antibodies to A, B, AB or O blood types and they are sometimes called universal
acceptors because of this.
The respiratory system moves gases
The organs of the respiratory system consist of those that form a pathway to the lungs and
the lungs, where gas (O a2d CO ) ex2hange occurs.
The upper respiratory tract prepares air
Air is warmed and filtered (mucus traps) in the nose, then moves across the pharynx to
pass through the glottis into the larynx. It helps to warm and moisten the air going to the
lungs. The epiglottis is flexible piece of tissue that covers the lungs during swallowing to
prevent blockage or entry of food/liquid into the lungs.
The lower respiratory tract is where gas exchange takes place
The cilia on the epithelial wall of the trachea sweeps impurities caught by mucus toward
the pharynx, where they can be swallowed and eliminated by the GI system. The trachea
leads to the bronchial tree, which branches into smaller bronchiole tubes (bronchi) and
leads to air sacs called alveoli. Gas exchange occurs in the alveoli. Alveoli are a single
layer of epithelial cells and are surrounded by capillaries, themselves a single cell layer
thick. This allows for efficient movement of O and2CO . 2
Mechanism and control of breathing or ventilation
During inspiration (inhalation), air comes into the lungs because the chest has expanded
due to contraction of key skeletal muscles, such as the diaphragm and intercostals,
creating a vacuum that draws air in. During expiration (exhalation), air leaves the lungs
because these muscles now relax and the chest returns to its normal size. Although
expiration is normally passive, it can also be forced with the use of muscles in the back,
neck, chest and stomach. (This is necessary to sing and blow out air.)
The respiratory center in the brain regulates breathing, which occurs automatically (~12-
20 breaths/minute), but is also subject to voluntary control. When the pH of the blood
lowers due to the increase in H , which can occur upon reduce breathing
(hypoventilation), chemoreceptors in the vasculature send signals to the center and the
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center sends signals to speed up breathing to help remove CO and e2change for O . The 2
reverse happens with hyperventilation.
Gases must exchange in the tissues
Diffusion (the partial pressure and solubility of a gas determines its concentration in the
body) of these gases drives the exchange, i.e. molecules move down their concentration
gradients in a tendency towards equilibrium. In the lungs, CO leave2 the RBC in the
blood at the capillaries around alveoli, and oxygen enters the RBC to be carried by
hemoglobin. In the tissue capillaries, O le2ves the RBC/blood, and CO – waste2product
from cellular respiration - enters the blood and is transported largely as bicarbonate ion.
The constantly active metabolic pathways guarantee that O is co2tinuously consumed
and that CO w2ste constantly builds up in tissues.
Respiration and health issues
Illnesses that affect the upper respiratory tract are not as serious as those that affect the
lower respiratory tract. Infections are the most common cause of disease in the
respiratory tract. Asthma is a disease of the bronchi and bronchioles that is marked by an
unusual sensitivity to specific irritants and overactive lung inflammation and constriction
of airways. Emphysema is loss of lung elasticity and functional alveoli, while COPD is a
suite of ailments that occur chronically: emphysema, bronchitis, and asthma.
Overview of digestion
The gastrointestinal tract (GI tract) contains a number of organs that carry out several
processes as they digest food. The wall of the GI tract typically has four layers and is
modified in each of the organs. Several accessory organs participate in food digestion
and the system is controlled by input from the nervous system and hormones (...as are all
the organ systems).
Digestion organs and process
The mouth receives food where it is chewed as physical and chemical digestion begins.
Secretions by the salivary glands (amylase) begin carbohydrate digestion before food
enters the pharynx and the esophagus. A bolus of food travels by peristalsis to the
The stomach has a very low pH (due to secretion of hydrochloric acid, HCl), which
activates pepsin (a protease) as well as helping to destroy bacteria. The stomach stores
food and continues chemical digestion which is completed in the small intestine. The
stomach passes on its contents, known as chyme and the products of digestion are
absorbed by the small intestine, with its undulating walls covered by villi and microvilli
to increase surface area for absorption of nutrients into the blood or into the lymph.
Blood vessels remove sugars, amino acids, nucleotides from the small intestine, while
fatty acids are removed by the lymph vessels (lacteals). Blood with absorbed nutrients
from the small intestines travels via the hepatic portal system for further metabolic
conversion and/or storage by the liver.
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Three accessory organs are crucial for digestion and absorption
The pancreas produces pancreatic juice (lipase, amylase and trypsin enzymes), which is
sent to the small intestine for the chemical digestion of food, (this is an exocrine gland
function of the pancreas). The pancreas also secretes sodium bicarbonate (NaHCO ) to
neutralize the acidic pH of the stomach contents (recall also the buffering function of
bicarbonate in the blood).
The liver is a major metabolic organ, which stores glucose as glycogen and produces bile,
which is derived from cholesterol and bilirubin (bilirubin is a breakdown product of
hemoglobin). Iron and several vitamins (fat soluble especially) are stored in the liver.
The liver also detoxifies many substances that arrive via the bloodstream. The liver also
makes many important blood proteins. Hepatitis and cirrhosis of the liver are diseases
that can compromise many of these important functions of the liver.
Bile is stored in the gallbladder before it is sent to the small intestine for emulsification of
fats to aid in their transport, absorption and metabolism. Gallstones are often made of
cholesterol crystals and can block bile transport to the small intestines.
The large intestine and defecation
The large intestine absorbs water, salts and a few vitamins produced by bacteria that
normally reside here, and it carries out defecation or expulsion of undigested food
remains. Sphincter muscles (smooth muscle category) under involuntary and voluntary
control are responsible for bowel movements.
Nutrition needs and your diet
Nutrients are components of food that are used by the body to carry out its various
functions. Body mass index (BMI) is a simple measure of body proportions that help to
gauge a person’s overall proportions and is an indirect and imprecise measure of fitness.
Carbohydrates, proteins, lipids, minerals and vitamins are major classes of nutrients
needed by our bodies. Based on the amount we need to consume to support homeostasis,
the first three are considered macronutrients and the last two micronutrients.
Carbohydrates are the preferred energy source for energy production/storage by our body.
Carbohydrates come in simple (monosaccharide, disaccharide) or complex forms
(polysaccharides). Excessive carbohydrate intake can result in hyperglycemia, a
condition that can result in diabetes if persistent and may lead to overweight or obese
Proteins are made from amino acids, several of which are not made by our bodies and are
therefore required in our diet and are thus termed essential amino acids. Since proteins
are not effectively stored we generally need to ingest some amount daily, while excessive
protein intake results in chronic excretion of nitrogenous wastes and can overwork
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Lipids are needed by our bodies, and can be used an energy source and a form of stored
energy. They have about twice the calories that an equivalent amount of carbohydrates
or proteins possess. An excess of lipid intake is linked to obesity, while saturated fats
(especially the trans-fat variety) and cholesterol contribute to atherosclerosis and
cardiovascular disease. HDL (high density lipoprotein) is a ‘good’ form of packaged
cholesterol that is removed from the blood stream by the liver, while LDL (low density
lipoprotein) is the form that contributes to atherosclerosis and CVD.
Mineral and vitamins contribute to important body processes, but are typically needed in
small amounts in our diet and can be supplied adequ