Negative and Positive Feedback Loops
Control hormone levelsNegative feedback loopHormone release stops in response to decrease in stimulus- Stimulus (eating) raises blood glucose levels- Pancreas releases insulin in response to elevated blood glucose- Blood glucose decreases as it is used by the body or stored in the liver - Insulin release stops as blood glucose levels normalize
Positive feedback loop As long as stimulus is present, action of hormone continues- Infant nursing at mother’s breast→stimulates hypothalamus→stimulates posterior pituitary- Oxytocin released→stimulates milk production and ejection from mammary glands- Milk release continues as long as infant continues to nurse
The Major Endocrine OrgansThe major endocrine organs of the body include: the pituitary, pineal, thyroid, parathyroid, thymus, and adrenal glands, pancreas, and gonads (ovaries and testes)Endocrine glands - Ductless - Release hormones - Directly into target tissues - Into bloodstream to be carried to target tissuesHormones(Greek word hormone – to set into motion)
Pituitary Gland and Hypothalamus
o The pituitary gland is approximately the size of a pea.
o It hangs by a stalk from the inferior surface of the hypothalamus of the brain, where it is snugly surrounded by the sella turcica of the sphenoid bone.
o It has two functional lobes – the anterior pituitary (glandular tissue) and the posterior pituitary (nervous tissue).
o The anterior pituitary gland controls the activity of so many other endocrine glands (“master endocrine gland”)
o The release of each of its hormones is controlled by releasing hormones and inhibiting hormones produced by the hypothalamus.
o The hypothalamus also makes two additional hormones, oxytocinand antidiuretic hormone, which are transported along the axons of the hypothalamic nuerosecretory cells to the posterior pituitary for storage. They are later released into the blood in response to nerve impulses from the hypothalamus.
Oxytocin
o Is released in significant amounts only during childbirth and nursing.
o It stimulates powerful contractions of the uterine muscle during sexual relations, during labor, and during breastfeeding.
o It also causes milk ejection (let-down reflex) in a nursing woman.
Antidiuretic Hormone (ADH)
o ADH is a chemical that inhibits or prevents urine production.
o ADH causes the kidneys to reabsorb more water from the forming urine; as a result, urine volume decreases, and blood volume increases.
o In larger amounts, ADH also increases blood pressure by causing constriction of the arterioles (small arteries). For this reason, it is sometimes referred to as vasopressin.
Anterior Pituitary HormonesThe anterior pituitary produces several hormones that affect many body organs. Growth Hormone (GH)
o Its major effects are directed to the growth of skeletal muscles and long bones of the body
o At the same time, it causes fats to be broken down and used for energy while it spares glucose, helping to maintain blood sugar homeostasis.
ProlactinIts only known target in humans is the breast.After childbirth, it stimulates and maintains milk production by the mother’s breasts.Gonadotropic Hormones (FSH and LH)
o Regulate the hormonal activity of the gonads (ovaries and testes)
o In women, the FSH stimulates follicle development in the ovaries.
o In men, FSH stimulates sperm production by the testes.
o LH triggers ovulation of an egg from the ovary and causes the ruptured follicle to produce progesterone and some estrogen.
o LH stimulates testosterone production by the interstitial cells of the testes.
Pineal Gland
The pineal gland is a small, cone-shaped gland that hangs from the roof of the third ventricle of the brain.
Melatonin
o The only hormone secreted from pineal gland in substantial amounts
o Believed to be a “sleep trigger” that plays an important role in establishing the body’s sleep-wake cycle.
o The level of melatonin rises and falls during the course of the day and night.
o The peak level occurs at night and makes us drowsy
o The lowest level occurs during daylight around noon.
Thyroid Gland
• The thyroid gland is located at the base of the throat, just inferior to the Adam’s apple.
• It is a fairly large gland consisting of two lobes joined by a central mass, or isthmus.
• The thyroid gland makes two hormones, one called thyroid hormone, the other called calcitonin.
Thyroid Hormone
o Referred to as body’s major metabolic hormone
o Contains two active iodine-containing hormones, thyroxine (T4)and thriiodothyronine (T3)
o Most triiodothyronine is formed at the target tissues by conversion of thyronine to triiodothyronine
o Thyroid hormone controls the rate at which glucose is “burned”, or oxidized, and converted to body heat and chemical energy (ATP).
o Thyroid hormone is also important for normal tissue growth and development, especially in the reproductive and nervous systems.
Homeostatic Imbalance
➢ Without iodine, functional thyroid hormones cannot be made.
➢ The source of iodine is our diet (seafoods)
➢ Goiter is an enlargement of the thyroid gland that results when the diet is deficient in iodine.
Hyposecretion of thyroxine may indicate problems other than iodine deficiency. If it occurs in early childhood, the result is cretinism.
▪ Results in dwarfism and mental retardation (if discovered early, hormone replacement will prevent mental impairment)
Hypothyroidism occurring in adults results in myxedema
▪ Characterized by both physical and mental sluggishness (no mental impairment)
▪ Other signs are puffiness of the face, fatigue, poor muscle tone, low body temperature, obesity, and dry skin (Oral thyroxine is prescribed to treat this condition)
➢ Hyperthyroidism generally results from a tumor of the thyroid gland.
➢ Extreme overproduction of thyroxine results in a high basal metabolic rate, intolerance of heat, rapid heartbeat, weight loss, nervous and agitated behavior, and a general inability to relax.
Graves’ disease
o A form of hyperthyroidism
o The thyroid gland enlarges, the eyes bulge (exophthalmos)
Calcitonin
➢ Second important hormone product of the thyroid gland
➢ Decreases the blood calcium ion level by causing calcium to be deposited in the bones
Parathyroid Glands
➢ The parathyroid glands are tiny masses of glandular tissue most often on the posterior surface of the thyroid gland.
➢ Parathyroid hormone (PTH) is the most important regulator of calcium ion homeostasis of the blood.
➢ Although the skeleton is the major PTH target, PTH also stimulates the kidneys and intestine to absorb more calcium ions.
Homeostatic Imbalance
o If blood calcium ion level falls too low, neurons become extremely irritable and overactive. They deliver impulses to the muscles so rapidly that the muscles go into uncontrollable spasms (tetany), which may be fatal.
o Severe hyperparathyroidism causes massive bone destruction. The bones become very fragile, and spontaneous fractures begin to occur.
Thymus
o Is located in the upper thorax, posterior to the sternum.
o Large in infants and children, it decreases in size throughout adulthood.
o By old age, it is composed mostly of fibrous connective tissue and fat.
o The thymus produces a hormone called thymosin and others that appear to be essential for normal development of a special group of white blood cells (T lymphocytes) and the immune response.
Adrenal Glands
o The two adrenal glands curve over the top of the kidneys like triangular hats.
o It is structurally and functionally two endocrine organs in one.
• it has parts made of glandular (cortex) and neural tissue (medulla)
• The central medulla region is enclosed by the adrenal cortex, which contains three separate layers of cells.
Hormones of the Adrenal CortexThe adrenal cortex produces three major groups of steroid hormones, collectively called corticosteroids:
1. Mineralocorticoids (aldosterone)
➢ Are produced by the outermost adrenal cortex cell layer.
➢ Are important in regulating the mineral (salt) content of the blood, particularly the concentrations of sodium and potassium ions.
➢ These hormones target the kidney tubules(Distal Convulating Kidney Tubles) that selectively reabsorb the minerals or allow them to be flushed out of the body in urine.
➢ When the blood level of aldosterone rises, the kidney tubule cell reabsorb increasing amounts of sodium ions and secrete more potassium ions into the urine.
➢ When sodium is reabsorbed, water follows. Thus, the mineralocorticoids help regulate both water and electrolyte balance in body fluids.
2. Glucocorticoids (Cortisone and Cortisol)
➢ Glucocorticoids promote normal cell metabolism and help the body to resist long-term stressors, primarily by increasing the blood glucose level.
➢ When blood levels of glucocorticoids are high, fats and even proteins are broken down by body cells and converted to glucose, which is released to the blood.
➢ For this reason, glucocorticoids are said to be hyperglycemic hormones.
➢ Glucocorticoids also seem to control the more unpleasant effects of inflammation by decreasing edema, and they reduce pain by inhibiting the pain-causing prostaglandins.
➢ Because of their anti-inflammatory properties, glucocorticoids are often prescribed as drugs to suppress inflammation for patients with rheumatoid arthritis.
➢ Glucocorticoids are released from the adrenal cortex in response to a rising blood level of ACTH (Adrenocorticotropic hormone).
3. Sex Hormones
➢ In both men and women, the adrenal cortex produces both male and female sex hormones throughout life in relatively small amounts.
➢ The bulk of the sex hormones produced by the innermost cortex layer are androgens (male sex hormones), but some estrogens (female sex hormones) are also formed.
Homeostatic Imbalance1. Addisson’s disease (hyposecretion of all the adrenal cortex hormones)
✓ Bronze tone of the skin (suntan)
✓ Na (sodium) and water are lost from the body
✓ Muscles become weak and shock is a possibility
✓ Hypoglycemia (↓ glucocorticoids)
✓ Suppression of the immune system
2. Hyperaldosteronism (hyperactivity of the outermost cortical area)
✓ Excessive water and sodium ions retention
✓ High blood pressure
✓ Edema
✓ Low potassium ions level (hypokalemia)
3. Cushing’s Syndrome (Excessive glucocorticoids)
✓ Swollen “moon face” and “Buffalo hump”
✓ High blood pressure and hyperglycemia (steroid diabetes)
✓ Weakening of the bones (as protein is withdrawn to be converted to glucose)
✓ Severe depression of the immune system
4. Hypersecretion of the sex hormones leads to masculinization, regardless of sex.
Hormones of the Adrenal Medulla
➢ When the medulla is stimulated by sympathetic nervous system neurons, its cells release two similar hormones, epinephrine(adrenaline) and norepinephrine (noradrenaline), into the bloodstream.
➢ Collectively, these hormones are called catecholamines.
➢ The catecholamines of the adrenal medulla prepare the body to cope with short-term stressful situations and cause the so-called alarm stage of the stress response.
➢ Glucocorticoids, by contrast, are produced by the adrenal cortex and are important when coping with prolonged or continuing stressors, such as dealing with the death of a family member or having a major operation (resistance stage).
Pancreatic Islets
➢ The pancreas, located close to the stomach in the abdominal cavity, is a mixed gland.
➢ The pancreatic islets, also called the islets of Langerhans, are little masses of endocrine (hormone-producing) tissue of the pancreas.
➢ The exocrine, or acinar, part of the pancreas acts as part of the digestive system.
➢ Two important hormones produced by the islet cells are insulin and glucagon.
Insulin
➢ Hormone released by the beta cells of the islets in response to a high level of blood glucose.
➢ Acts on all body cells, increasing their ability to import glucose across their plasma membranes.
➢ Insulin also speeds up these “use it” or “store it” activities.
➢ Because insulin sweeps the glucose out of the blood, its effect is said to be hypoglycemic.
➢ Without it, essentially no glucose can get into the cells to be used.
Glucagon
➢ Acts as an antagonist of insulin
➢ Released by the alpha cells of the islets in response to a low blood glucose levels.
➢ Its action is basically hyperglycemic.
➢ Its primary target is the liver, which it stimulates to break down stored glycogen to glucose and to release the glucose into the blood.
Gonads
➢ The female and male gonads produce sex cells.
➢ They also produce sex hormones that are identical to those produced by adrenal cortex cells.
➢ The major differences from the adrenal sex hormone production are the source and relative amounts of hormones produced.
Hormones of the OvariesBesides producing female sex cells (ova, or eggs), ovaries produce two groups of steroid hormones, estrogens and progesterone.
1. Estrogen (Steroid Hormone)
➢ Responsible for the development of sex characteristics in women (primarily growth and maturation of the reproductive organs) and the appearance of secondary sex characteristics at puberty.
➢ Acting with progesterone, estrogens promote breast development and cyclic changes in the uterine lining (the menstrual cycle)
2. Progesterone (Steroid Hormone)
➢ Acts with estrogen to bring about the menstrual cycle.
➢ During pregnancy, it quiets the muscles of the uterus so that an implanted embryo will not be aborted and helps prepare breast tissue for lactation.
Hormones of the TestesIn addition to male sex cells, or sperm, the testes also produce male sex hormones, or androgens, of which testosterone is the most important.
3. Testosterone
➢ Promotes the growth and maturation of the reproductive system organs to prepare the young man for reproduction.
➢ It also causes the male’s secondary sex characteristics to appear and stimulates the male sex drive.
➢ It is necessary for continuous production of sperm.
➢ Testosterone production is specifically stimulated by LH.
Other Hormone-Producing Tissues and OrgansPlacenta
➢ During very early pregnancy, a hormone called human chorionic gonadotropin (hCG) is produced by the developing embryo and then by the fetal parts of the placenta.
➢ hCG stimulates the ovaries to continue producing estrogen and progesterone so that the lining of the uterus is not sloughed off in menses.
➢ In the third month, the placenta assumes the job of the ovaries of producing estrogen and progesterone, and the ovaries become inactive for the rest of the pregnancy.
➢ The high estrogen and progesterone blood levels maintain the lining of the uterus and prepare the breasts for producing milk.
➢ Human placental lactogen (hPL) works cooperatively with estrogen and progesterone in preparing the breasts for lactation.
➢ Relaxin, another placental hormone, causes the mother’s pelvic ligaments and the pubic symphysis to relax and become more flexible, which eases birth passage.
Developmental Aspects of the Endocrine System
➢ In late middle age, the efficiency of the ovaries begins to decline, causing menopause.
o Reproductive organs begin to atrophy
o Ability to bear children ends
o Problems associated with estrogen deficiency begin to occur (arteriosclerosis, osteoporosis, decreased skin elasticity, “hot flashes”)
➢ No such dramatic changes seem to happen in men.
➢ Elderly persons are less able to resist stress and infection.
➢ Exposure to pesticides, industrial chemicals, dioxin, and pother soil and water pollutants diminishes endocrine function, which may explain the higher cancer rates among older adults in certain areas of the country.
➢ All older people have some decline in insulin production, and type 2 diabetes mellitus is most common in this age group.
BLOOD
➢ It is the only fluid tissue in the body.
➢ A homogenous liquid that has both solid and liquid components.
➢ Taste, Odor, 5x thicker than water
➢ Classified as a connective tissue
❖Living cells = formed elements
❖Non-living matrix = plasma (90% water)
Components
•Formed elements (blood cells)are suspended in plasma
•The collagen and elastin fibers typical of other connective
tissues are absent from blood; instead, dissolved proteins
become visible as fibrin strands during blood clotting
•If a sample of blood is separated, the plasma rises to the
top, and the formed elements, being heavier, fall to the
bottom.
•Most of the erythrocytes (RBCs) settle at the bottom of the tube
•There is a thin, whitish layer called the buffy coat at the
junction between the erythrocytes and the plasma
containing leukocytes (WBCs) and platelets
Physical Characteristics and Volume
• Color range
➢ Oxygen-rich blood is scarlet red
➢ Oxygen-poor blood is dull red
• pH must remain between 7.35–7.45
• Slightly alkaline
• Blood temperature is slightly higher than body
temperature
• 5-6 Liters or about 6 quarts /body
Functions and Composition of Blood
1. Transport of gases, nutrients and waste
products
2. Transport of processed molecules
3. Transport of regulatory molecules
4. Regulation of pH and osmosis
5. Maintenance of body temp
6. Protection against foreign substances
7. Clot formation
Plasma
• The liquid part of the blood; 90 percent water
• Over 100 different substances are dissolved in this
straw-colored fluid:
➢ nutrients
➢ electrolytes
➢ respiratory gases
➢ hormones
➢ plasma proteins; and
➢ various wastes and products of cell metabolism
• Plasma proteins are the most abundant solutes in
plasma (albumin and clotting proteins)
• Plasma helps to distribute body heat, a by-product
of cellular metabolism, evenly throughout the body.
Formed Elements
Erythrocytes (RBCs)
• Function primarily to ferry oxygen to all cells of the body.
• RBCs differ from other blood cells because they are
anucleate (no nucleus)
• Contain very few organelles (RBCs circulating in the blood are literally “bags” of hemoglobin molecules )
•Very efficient oxygen transporters (they lack mitochondria and make ATP by anaerobic mechanisms)
• Their small size and peculiar shape provide a large surface area relative to their volume, making them suited for gas exchange
• RBCs outnumber WBCs by about 1,000 to 1 and are the
major factor contributing to blood viscosity.
• There are normally about 5 million cells per cubic millimeter of blood.
• The more hemoglobin molecules the RBCs contain, the more oxygen they will be able to carry.
• A single RBC contains about 250 million hemoglobin
molecules, each capable of binding 4 molecules of oxygen.
• Normal hemoglobin count is 12-18 grams of hemoglobin per 100 ml of blood
• Men: 13-18g/ml Women: 12-16 g/ml
Homeostatic Imbalance
Anemia
• a decrease in the oxygen-carrying ability of the blood,
whatever the reason is.
• May be the result of (1) a lower-than-normal number of
RBCs or (2) abnormal or deficient hemoglobin content in
the RBCs.
Polycythemia Vera
• An excessive or abnormal increase in the number of
erythrocytes; may result from bone marrow cancer or a
normal physiologic response to living at high altitudes,
where the air is thinner and less oxygen is available
(secondary polycythemia)
Formed Elements
Leukocytes (WBCs)
• Are far less numerous than RBCs
• They are crucial to body defense
• On average, there are 4,800 to 10,800 WBCs/mm3 of blood
• WBCs contain nuclei and the usual organelles, which makes them the only complete cells in the blood.
• WBCs are able to slip into and out of the blood vessels – a process called diapedesis
• WBCs can locate areas of tissue damage and infection in the body by responding to certain chemicals that diffuse
from the damaged cells (positive chemostaxis)
• Whenever WBCs mobilize for action, the body speeds up their production, and as many as twice the normal number of WBCs may appear in the blood within a few hours.
• A total WBC count above 11,000 cells/mm3 is referred to as leukocytosis.
• The opposite condition, leukopenia, is an abnormally low WBC count (commonly caused by certain drugs, such as corticosteroids and anti-cancer agents)
• WBCs are classified into two major groups – granulocytes
and agranulocytes – depending on whether or not they
contain visible granules in their cytoplasm.
Granulocytes
Neutrophils
➢ Are the most numerous WBCs.
➢ Neutrophils are avid phagocytes at sites of acute infection.
Eosinophils
➢ Their number increases rapidly during infections by parasitic worms ingected in food such as raw fish or entering through the skin.
Basophils
➢ The rarest of the WBCs, have large histamine-containing granules.
Histamine
➢ is an inflammatory chemical that makes blood vessels leaky and attracts other WBCs to the inflamed site
Agranulocytes
Lymphocytes
➢ Have a large, dark purple nucleus that occupies most of the cell volume.
➢ Lymphocytes tend to take up residence in lymphatic tissues, such as the tonsils, where they play an important role in the immune response.
➢ They are the second most numerous leukocytes in the blood
Monocytes
➢ Are the largest of the WBCs.
➢ When they migrate into the tissues, they change into macrophages.
➢ Macrophages are important in fighting chronic infections, such as tuberculosis, and in activating lymphocytes
Platelets
➢ They are fragments of bizarre multinucleate cells called megakaryocytes, which pinch off thousands of anucleate platelet “pieces” that quickly seal themselves off from the surrounding fluids.
➢ Normal adult has 150,000 to 450,000 per cubic millimeter of blood
➢ Platelets are needed for the clotting process that stops blood loss from broken blood vessels.
➢ Average lifespan is 9 to 12 days
Hematopoiesis
• Occurs in red bone marrow, or myeloid tissue.
• In adults, this tissue is found chiefly in the axial skeleton, pectoral andpelvic girdles, and proximal epiphyses of the humerus and femur.
• On average, the red marrow turns out an ounce of new bloodcontaining 100 billion new cells every day.
• All the formed elements arise from a common stem cell, thehemocytoblast, which resides in red bone marrow.
• Once a cell is committed to a specific blood pathway, it cannotchange.
• The hemocytoblast forms two types of descendants – the lymphoidstem cell, which produces lymphocytes, and the myeloid stem cell,which can produce other classes of formed elements.
Formation of RBCs
• Because they are anucleate, RBCs are unable to synthesizeproteins, grow, or divide.
• As they age, RBCs become rigid and begin to fall apart in 100 to 120 days.
• Their remains are eliminated by phagocytes in the spleen, liver, and other body tissues.
• RBC components are salvaged. Iron is bound to protein as ferritin, and the balance of the heme group is degraded to bilirubin, which is then secreted into the intestine by liver cells where it becomes a brown pigment called stercobilin that leaves the body in feces.
• Globin is broken down to amino acids which are released into the circulation.The rate of erythrocyte production is controlled by a hormone
called erythropoietin (from the kidneys)
• Erythropoietin targets the bone marrow prodding it into “high gear” to turn out more RBCs.
• An overabundance of erythrocytes, or an excessive amount of oxygen in the bloodstream, depresses erythropoietin release and RBC production.
• However, RBC production is controlled not by the relative number of RBCs in the blood, but by the ability of the available RBCs to transport enough oxygen to meet the body’s demands
Formation of WBCs and Platelets
• The formation of leukocytes and platelets is stimulated by hormones
• These colony stimulating factors (CSFs) and interleukins not only prompt red bone marrow to turn out leukocytes, but also enhance the ability of mature leukocytes to protect the body.
• The hormone thrombopoietin accelerates the production of platelets from megakaryocytes, but little is know about how process is regulated.
• When bone marrow problems or disease condition is
suspected, bone marrow biopsy is done.
Hemostasis
If a blood vessel wall breaks, a series of reactions
starts the process of hemostasis (stopping the
bleeding).
Phases of Hemostasis
1. Vascular spasms occur.
2. Platelet plug forms.
3. Coagulation events occur.
Human Blood Groups
• An antigen is a substance that the body
recognizes as foreign; it stimulates the
immune system to mount a defense against
it.
• The “recognizers” are antibodies present in
plasma that attach to RBCs bearing surface
antigens different from those on the patient’s
RBCs.
ABO and Rh Blood Types
The blood group system recognizes four blood types:
• Type A, B, AB, and O
• They are distinguished from each other in part by their antigens and antibodies.
• Specific antibodies are found in the serum based on the type of antigen on the surface of the RBC
ABO and Rh Blood Types
BLOOD TYPE Can Accept From Can Donate To
A A, O A, AB
B B, O B, AB
AB A, B, AB, O AB
O O O, A, B, AB
The Rh Factor
Rh-Positive Rh-Negative
Contains the Rh antigen -No Rh antigen
-Will make antibodies
if given Rh-positive
blood
-Agglutination can
occur if given Rh-positive blood
Summary
• Blood is responsible for transporting oxygen, fluids,
hormones, and antibodies and for eliminating waste
materials.
• The major components of blood include the formed elements and plasma.
• RBCs transport oxygen and carbon dioxide; WBCs destroy foreign invaders.
• WBCs include granulocytes and agranulocytes.
• Plasma is the liquid portion of unclotted blood. Serum is the liquid portion of clotted blood
• Hemostasis includes four stages: blood vessel spasm,
platelet plug formation, blood clotting, and fibrinolysis.
• ABO and Rh types are determined by the antigen found
on the RBCs
Updated 140d ago
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