BIO 2402 Exam 1 2.04.18 PM PDF

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Exam 1 Introduction   

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Anatomy – studies the structure of body parts and their relationships to one another Physiology – concerns the function of the body, in other words, how the body parts work and carry out their life-sustaining activities. Homeostasis – the condition of maintaining the body’s internal environment in a relative constant state (steady temp, blood pressure, glucose levels, etc. …) (homeostasis is a ceaseless process of activities in response to stresses in an attempt to maintain equilibrium) Homeostatic imbalance – anything that disturbs or alters the balance of the internal environment Homeostatic control mechanisms – are those “mechanisms” which are generally “selfregulating” and serve to maintain the homeostatic “steady state.” Regardless of the factor or event being regulated, all homeostatic control mechanisms are processes involving at least three components that work together. o Receptor (sensor) – monitors the environment and responds to changes by sending information to the control center o Control center (brain) – determines the set point, which is the level or range at which a variable is to be maintained o Effector (nervous system or endocrine system) – provides the means for the control center’s response (output) to the stimulus Negative Feedback – The output shuts off the original effect of the stimulus or reduces its intensity. A change in one direction results in a feedback that causes a change or adjustment in the opposite direction. o This is how most homeostatic control mechanisms function; similar to a thermostat. o Endocrine system – pancreas produces insulin and glucagon Positive Feedback – The result or response enhances the original stimulus so that the response is accelerated. A change in one direction accelerates more change in the same direction. o Rare in life; blood clotting, labor contractions, orgasm

Regulatory systems involved with feedback mechanisms:  

The “Input” and “Output” amounts to “messages” between body parts… These messages can be conducted either electrically or chemically The two regulatory systems involved: o Nervous System – uses “electrical impulses delivered by neurons to specific target cells  Neural control is quick, brief, and generally results in either muscle contraction or gland secretion.

o Endocrine System – affects cell activity by releasing chemically messengers (hormones) directly into the blood system.  The target cells are varied (might be all over the body)  Hormonal control takes from minutes to hours and the changes are long lasting (slow, long lasting)

Endocrine System   

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Endocrine system acts with nervous system to coordinate and integrate activity of body cells Influences metabolic activities via hormones transported in blood o Hormones usually made of protein Endocrine system controls and integrates: o Reproduction o Growth & Development o Maintenance of electrolyte, water, and nutrient balance of blood o Regulation of cellular metabolism and energy balance o Mobilization of body defenses Types of Glands o Endocrine Glands – secrete their products into extracellular (outside cell) spaces where they are picked up and transported by the circulatory system  Ex: Pineal Gland, Hypothalamus, Pituitary gland, Thyroid gland, Parathyroid glands (on dorsal aspect of thyroid gland), Thymus, Adrenal glands, Pancreas, Gonads (Ovary – female, Testis – male) o Exocrine Glands – produce nonhormonal substances and secrete products by way of a duct (tube), onto a surface.  Ex: salivary, sweat, and digestive glands

Hormones 

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Hormones – a secretion that is transported in the blood (or lymph) and alters the physiological activity of a target cell(s); A chemical messenger produced by one type of cell which has a specific effect on the metabolic activity of another type of cell Two main classes of Hormones o Amino Acid based molecules – ranging from small amino acids to huge proteins  Are usually water-soluble and cannot cross the plasma membrane  Includes the majority of hormones o Steroids (derivatives of cholesterol)  Are lipid soluble and therefore can dissolve in and cross the plasma membrane  Includes only gonadal and some adrenal hormones Mechanism of hormonal action – Since hormones are circulated in the blood stream, virtually all tissues are exposed to them. However, any given hormone only influences the activities of specific target tissues. Why? o Cells only respond to a hormone if they have specific receptors for that hormone

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 Receptors are large proteins found mostly on the cell’s surface  Receptors bind with specific hormones (lock and key analogy) only o When a hormone binds to the receptor, it causes a chain of events within the cell which results in some physiological change (the hormones effect) o A single hormone can produce different effects on different cells because there might be either  Different receptors  Varying quantities of receptors producing various magnitudes of an effect Hormone Effects – A hormone typically produces one or more of the following changes: o Alters plasma membrane permeability (or membrane potential) by opening or closing ion channels o Stimulates synthesis of enzymes and other proteins within the cells (starts/stops protein synthesis) o Activate/deactivate enzymes o Induce secretory activity (glands secreting) o Stimulate mitosis Action of Hormones – Hormones act in one of two ways, depending on their chemical nature and receptor location o Water-soluble hormones (all amino acid-based hormones except thyroid hormone)  Act on plasma membrane receptors  Act via G protein second-messengers  Cannot enter cell o Lipid-soluble hormones (steroid and thyroid hormones)  Act on intracellular receptors that directly activate genes  Can enter cell Plasma Membrane Receptors and Second-Messenger Systems o Amino acid-based hormones, except thyroid hormone, exert effects through second-messenger systems o Two main second-messenger systems:  Cyclic AMP  PIP2-calcium  PIP2 is split into DAG and IP3  Calcium ions are released Intracellular Receptors and Direct Gene Activation o Lipid-soluble steroid hormones and thyroid hormones and thyroid hormone can diffuse into target cells and bind with intracellular receptors o Receptor hormone complex enters nucleus and binds to specific region of DNA o Helps initiate DNA transcription to produce mRNA o mRNA is then translated into specific protein  Proteins synthesized have various functions  Examples: metabolic activities, structural purposes, or exported from cell

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Endocrine Gland Stimuli o Endocrine glands are stimulated to synthesize and release hormones in response to one of three stimuli:  Humoral stimuli (fluid - blood)  Changing blood levels of ions and nutrients directly stimulate secretion of hormones  Example: Ca2+ in blood o Declining blood Ca2+ concentration stimulates parathyroid glands to secrete PTH (parathyroid hormone) o PTH causes Ca2+ concentrations to rise, and stimulus is removed)  Neural stimuli (neurons and nerve cells)  Nerve fibers stimulate hormone release o Sympathetic nervous system fibers stimulate adrenal medulla to secrete catecholamines  Hormonal stimuli (hormones from other endocrine glands)  Hormones stimulate other endocrine organs to release their hormones o Hypothalamic hormones stimulate release of most anterior pituitary hormones o Anterior pituitary hormones stimulate targets to secrete still more hormones o Hypothalamic-pituitary-target endocrine organ feedback loop  Hormones from final target organs inhibit release of anterior pituitary hormones

Nervous System Modulation  

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Nervous system can make adjustments to hormone levels when needed o Can modify stimulation or inhibition of endocrine glands Nervous system can override normal endocrine controls o Example: under severe stress, hypothalamus and sympathetic nervous system override insulin to allow blood glucose levels to increase  Prepares body for “fight or flight” Half-life, Onset, and Duration of Hormonal Activity o Steroids and thyroid hormone are attached to plasma proteins o All others are water soluble and circulate without carriers o Blood is 90% water, so lipid-soluble steroid and thyroid hormones have trouble mixing with and traveling in the blood.  To get around, the hormones attach to water soluble proteins that shuttle them in the blood’s aqueous environment (http://e.hormone.tulane.edu/learning/deliver-transport-proteins.html) o Concentration of circulating hormone reflects:

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Rate of release Speed at which it is inactivated and removed from body

o Removal  Hormones can be removed from blood by:  Kidneys or Liver o Half-life: time required for level of hormone in blood level to decrease by half  Varies anywhere from fraction of a minute to a week, depending on hormone o Onset  Hormones have different response times:  Some responses are immediate  Some, especially steroid, can take hours to days  Some are inactive until they enter target cells o Duration  The duration of response is usually limited  Ranges from 10 seconds to several hours  Effects may disappear rapidly as blood levels drop, but some may persist for hours at low blood levels Half-life, Onset, and Duration of Hormonal Activity o Interaction of Hormones at Target Cells  3 types of hormone interaction:  Permissiveness:  The situation in which one hormone cannot exert its full effects without another hormone being present  Example: reproductive hormones need thyroid hormone to have effect  Synergism:  Occurs when more than one hormone produces the same effects at the target cell and their combined effects are amplified  Example: glucagon and epinephrine both cause liver to release glucose  Antagonism:  Occurs when one hormone opposes the action of another  Example: insulin and glucagon  Endocrine Glands o Hypothalamus & Pituitary  Hypothalamus is connected to pituitary gland (hypophysis) via stalk called infundibulum (tells pituitary what to do)  Pituitary has 2 major lobes and secretes at least 8 major hormones

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Posterior pituitary: (neurohypophysis) composed of neural tissue (derived from a downgrowth of brain) that secretes neurohormones o Posterior lobe, along with infundibulum make up the neurohypophysis o Maintains neural connection to hypothalamus via hypothalamic-hypophyseal tract  Tract arises from neurons in nuclei in hypothalamus; runs through infundibulum o Secretes 2 neurohormones (Oxytocin and Antidiuretic hormone (ADH))  Hormones are stored in axon terminals in posterior pituitary and are released into blood when neurons fire  Oxytocin  Strong stimulant of uterine contractions released during childbirth  Also acts as hormonal trigger for milk injection, i.e., the “letdown” reflex in women whose breasts are producing milk in response to prolactin o Suckling causes a reflex-9nitiated release of oxytocin, which targets cells surrounding the milk-producing glands, causing them to contract and force milk from the breast into the infant’s mouth  Both are positive feedback mechanisms  Antidiuretic Hormone (ADH)  Hypothalamus contains osmoreceptors that monitor solute concentrations  If concentration too high, posterior pituitary triggered to secrete ADH  Targets kidney tubules to reabsorb more water to inhibit or prevent urine formation  Release also triggered by pain, low blood pressure, and drugs  Inhibited by alcohol, diuretics  High concentrations cause vasoconstriction  Homeostatic Imbalance  Diabetes insipidus o ADH deficiency due to damage to hypothalamus or posterior pituitary

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o Causes excess urination and thirst; must keep well hydrated  Syndrome of inappropriate ADH secretion (SIADH) o Retention of fluid, headache, disorientation o Fluid restriction; blood sodium level monitoring Anterior pituitary: (adenohypophysis) consists of glandular tissue derived from outpocketing of oral mucosa o Vascularly connected to hypothalamus via hypophyseal portal system o Hypothalamus secretes releasing and inhibiting hormones to anterior pituitary to regulate hormone secretion (major control system for endocrine system) o All 6 hormones are peptide hormones; All but 2 are tropic hormones (tropins) that regulate secretion of other hormones  Growth hormone (GH)  Also called somatropin as it is produced by somatatropic cells (cells that promote growth)  Has direct actions on metabolism and indirect growth-promoting actions o GH is essentially an anabolic (tissue building) hormone o Causes glycogen breakdown in liver and decreases the rate of glucose uptake and metabolism, conserving glucose; glucose “sparing action”, which raises blood glucose levels o Increases blood levels of fatty acids and encourages their use for fuel o Increases amino acid uptake into cells and their incorporation into proteins  GH stimulates most cells to enlarge and divide, but major targets are bone and skeletal muscle  Regulation of secretion o GH release or inhibition chiefly regulated by hypothalamic hormones on somatotropic cells

Growth hormone-releasing hormone (GHRH) stimulates GH release; Triggered by low blood GH or glucose, or high amino acid levels o Growth hormone-inhibiting hormone (GHIH) (somatostatin) inhibits release  Triggered by increase in GH and IGF levels; IGF=a protein, “insulin-like growth factor”, stimulates growth  Homeostatic Imbalance o Hypersecretion of GH is usually caused by anterior pituitary tumor  In children, results in gigantism; can reach heights of 8 feet  In adults, results in acromegaly [meg’]; overgrowth of hands, feet, and face o Hyposecretion of GH  In children, results in pituitary dwarfism; may reach height of only 4 feet  In adults, usually causes no problems Thyroid-stimulating hormone (TSH) (tropic)  Tropic hormone that is also called thyrotropin as it is produced by thyrotropic cells  Stimulates normal development and secretory activity of thyroid  Release triggered by thyrotropin-releasing hormone (TRH) from hypothalamus  Inhibited by rising blood levels of thyroid hormones that act on both pituitary and hypothalamus Adrenocorticotropic hormone (ACTH) (tropic)  Also called corticotropin as it is secreted by corticotropic cells  ACTH stimulates adrenal cortex to release corticosteroids 

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Regulation of ACTH release o Triggered by hypothalamic corticotropin-releasing hormone (CRH) in daily rhythm; highest levels in morning o Internal and external factors that alter release of CRH include fever, hypoglycemia, and stressors Gonadotropins (FSH and LH)  Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are secreted by gonadotropic cells of anterior pituitary  FSH stimulates production of gametes (egg or sperm)  LH promotes production of gonadal hormones o In females, LH helps mature follicles of egg, triggers ovulation and release of estrogen and progesterone o In males, LH stimulates production of testosterone  LH and FSH both are absent from blood in prepubertal boys and girls  Regulation of gonadotropin release o Triggered by gonadotropin-releasing hormone (GnRH) from the hypothalamus during and after puberty o Suppressed by gonadal hormones (feedback) o Prolactin (PRL)  Secreted by prolactin cells of anterior pituitary  Stimulates milk production in females; role in males not well understood  Regulation primarily controlled by prolactininhibiting hormone (PIH) from the hypothalamus, which is dopamine o PIH prevents release of PRL until needed, with decreased levels leading to lactation 

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Increased estrogen levels stimulate PRL o Reason behind breast swelling and tenderness during menstrual cycle PRL blood levels rise dramatically toward end of pregnancy Suckling stimulates PRL release and promotes continued milk production

o Thyroid Gland  Butterfly-shaped gland in anterior neck on trachea, just inferior to larynx, that consists of:  Follicles: hollow sphere of epithelial follicular cells that produce glycoprotein thyroglobulin  Colloid: fluid of follicle lumen containing thyroglobulin plus iodine and is precursor to thyroid hormone  Parafollicular cells: produce hormone calcitonin  Thyroid Hormone (TH)  Body’s major metabolic hormone  Found in two forms: T4 and T3, both are iodine-containing amine hormones  TH affects virtually every cell in body  Enters target cell and binds to intracellular receptors within nucleus o Triggers transcription of various metabolism genes  Effects of thyroid hormone include: o Increases basal metabolic rate and heat production o Regulates tissue growth and development o Maintains blood pressure  Thyroid gland stores hormone extracellularly in follicle lumen until triggered by TSH to release o When stimulated TH is produced by follicular cells  Homeostatic Imbalance o Hyposecretion of TH in adults can lead to myxedema  Due to lack of iodine, a goiter may develop  Lack of iodine decreases TH levels, which triggers increased TSH secretion, triggering thyroid to synthesize more and more unusable thyroglobulin  Thyroid enlarges o Hypersecretion of TH most common type is Graves’ disease  Autoimmune disease: body makes abnormal antibodies directed against thyroid follicular cells

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Antibodies mimic TSH, stimulating TH release Treatments include surgical removal of thyroid or radioactive iodine to destroy active thyroid cells

Calcitonin  Produced by parafollicular cells in response to high Ca2+ levels o Antagonist to parathyroid hormone (PTH)  No known physiological role in humans at normal physiological levels, but at higher-than-normal doses: o Inhibits osteoclast activity and prevents release of Ca2+ from bone matrix o Stimulates Ca2+ uptake and incorporation into bone matrix o 1-5% of minerals in bone exchange with extracellular fluid o Parathyroid Gland  4-8 tiny yellow-brown glands embedded in posterior aspect of thyroid  Contain parathyroid cells that secrete parathyroid hormone (PTH), or parathormone  PTH is most important hormone in Ca2+ homeostasis  Increases Ca2+ levels in blood  Secreted in response to low blood levels of Ca2+  Inhibited by rising levels of Ca2+  Target organs are skeleton, kidneys, and intestine  Parathyroid hormone functions to:  Stimulate osteoclasts to digest bone matrix and release Ca2+ to blood  Enhances reabsorption of Ca2+ and secretion of phosphate (PO43-) by kidneys  Promotes activation of vitamin D by kidneys, which leads to increased absorption of Ca2+ by intestinal mucosa 

o Adrenal glands  Paired, pyramid-shaped organs atop kidneys  Also referred to as suprarenal glands  Structurally and functionally it is two glands in one  Adrenal cortex: three layers of glandular tissue that synthesize and secrete several different hormones o This area of adrenal glands produces over 24 different hormones collectively called corticosteroids o Three layers of cortical cells produced by the different corticosteroids  Zona glomerulosa – Mineralocorticoids

Regulate electrolyte concentrations (primarily Na+ and K+) in extracellular fluid  Aldosterone: most potent mineralocorticoid o Stimulates Na + reabsorption by kidneys; results in increased blood volume and blood pressure o Stimulates K+ elimination by kidneys  Regulated hormonally (ACTH), humorally, and by renin-angiotensin-aldosterone mechanism  Zona fasciculata – Glucocorticoids  Influence metabolism of most cells and help us resist stressors  Keep blood glucose levels relatively constant  Maintain blood pressure by increasing action of vasoconstrictors  Glucocorticoid hormones include: o Cortisol (hydrocortisone); only glucocorticoid in significant amounts in humans o Prime metabolic effect is gluconeogenesis, formation of glucose from fats and proteins o Regulated hormonally (ACTH)  Zona reticularis – Gonadocorticoids (adre...