Download Discussion about endocrine system and more Summaries Nursing in PDF only on Docsity!
ANATOMY AND PHYSIOLOGY
ANATOMY OF THE ENDOCRINE SYSTEM
FUNCTION OF ENDOCRINE SYSTEM
Metabolism and tissue maturation Ion regulation Water balance Immune system regulation Heart rate and blood pressure regulation Control of blood glucose and other nutrients Control of reproductive function Urine contractions and milk release OVERVIEW- ENDOCRINE SYSTEM The body’s second great controlling system which influences metabolic activities of cells by means of hormones, which are produced by endocrine glands. Endocrine glands: pituitary, thyroid, parathyroid, adrenal, pineal, and thymus. The pancreas and gonads produce both hormones and exocrine products. The hypothalamus has both neural functions and releases hormones. OTHER TISSUES AND ORGANS THAT PRODUCES HORMONES Adipose cells (Adipocytes) Leptin, TFN/cytokines, plasminogen, angiotensin, adiponectin Small intestine CCK Stomach Gastrin, Gremlin (increase appetite and stimulate release of Growth Hormone), motilin Kidneys ADH and RAAS Heart ANH Both endocrine system and the nervous system regulate the activities of structures in the body, but they do so in different ways. The endocrine system is amplitude – modulated (a) whereas the nervous system is frequency – modulated (b). The response of target tissues to hormones is usually slower and of longer duration that of neurons. AMPLITUDE (HORMONES) Amplitude – modulated system. The concentration of the hormone determines the strength of the signal and the magnitude of the response. For most hormones, a small concentration of a hormone is a weak signal and produces a small response, whereas a larger concentration is a stronger signal and results in a greater response. FREQUENCY (NEURONS) Frequency – modulated system. The strength of the signal depends on the frequency, not the size, of the action potentials. All action potentials are the same size in a given tissue. A low frequency of action potentials is a weak stimulus, and a higher frequency is a stronger stimulus. FUNCTION OF ENDOCRINE SYSTEM
Negative – feedback mechanisms, which maintain homeostasis, control the secretion of most hormones. Hormone secretion from an endocrine tissue is regulated by one or more of these three mechanisms: Changes in the extracellular concentration of a non – hormone substances Stimulation by the nervous system Stimulation by a hormone from another endocrine tissue NEGATIVE FEEDBACK MECHANISM – MAINTENANCE OF EQUILIBRIUM Three basic components:
1. Sensor Receptors of stimulus 2. Control center Pituitary Hypothalamus 3. Effector Usually a tissue or a gland Stimulus – usually an imbalance POSITIVE FEEDBACK MECHANISMS A positive feedback mechanism enhances the original stimulus and to accelerate activity. Integrator triggers a move in the same direction triggering an “explosive” response. Positive feedback mechanisms are less common. Examples: o Blood clotting, childbirth (oxytocin) HORMONAL REGULATION Thyrotrophin – releasing hormone (TRH) is released from neurons in the hypothalamus and travels in the blood to the anterior pituitary gland. TRH stimulates the release of thyroid
- stimulating hormone (TSH) from the anterior pituitary gland. TSH travels in the blood to the thyroid gland. TSH stimulates the secretion of thyroid hormones from the thyroid gland into the blood. Thyroid hormones act on tissues to produce responses. Thyroid hormones also have negative – feedback effect on the hypothalamus and the anterior pituitary to inhibit both TRH secretion and TSH secretion. The negative feedback helps keep blood thyroid hormone levels within a narrow range. Stimulatory Inhibitory HORMONE TRANSPORT AND EXCRETION Hormones are dissolved in plasma or bind to plasma proteins. Water – soluble hormones Proteins, epinephrine, and norepinephrine Readily diffuse out of the blood They are quickly broken down by enzymes or are taken up by tissues These hormones regulate activities that have a rapid onset and a short duration
Hypothalamohypophyseal tract connects the hypothalamus and the posterior pituitary Hormones are produced in hypothalamic neurons The hormones move down the axons of the tract and are secreted from the posterior pituitary
1. Stimuli within the nervous system stimulate hypothalamic neurons to either increase or decrease their action potential frequency. 2. Action potentials are carried by axons of the hypothalamic neurons through the hypothalamo hypophyseal tract to the posterior pituitary. The axons of neurons store hormones in the posterior pituitary. 3. In the posterior pituitary gland, action potentials cause the release of hormones (red balls) from axon terminals into the circulatory system. 4. The hormones pass through the circulatory system and influence the activity of their target tissues (green arrow). 1. Stimuli within the nervous system increase or decrease the secretion of releasing hormones and inhibiting hormones (blue balls) from neurons. 2. Releasing hormones and inhibiting hormones pass through the hypothalamo hypophyseal portal system to the anterior pituitary. 3. Releasing hormones and inhibiting hormones leave capillaries, bind to membrane – bound receptors, and stimulate or inhibit the release of hormones (yellow square) from anterior pituitary cells. 4. Anterior pituitary hormones (yellow square) are carried in the blood to their target tissues (green arrow) which, in some cases, are other endocrine glands.
HORMONES OF THE HYPOTHALAMUS
Hormon es Structur e Target Tissue Respons e Growth hormone– releasing hormone (GHRH) Peptide Anterior pituitary cells that secrete growth hormone Increased growth hormone secretion Growth hormone- inhibiting hormone (GHIH), or somatost atin Small Peptide Anterior pituitary cells that secrete growth hormone decrease d growth hormone secretion Thyrotrop in- releasing hormone (TRH) Small Peptide Anterior- pituitary cells that secrete thyroid- stimulating hormone Increased thyroid- stimulatin g hormone secretion Corticotro pin- releasing hormone (CRH) Peptide Anterior pituitary cells that secrete adrenocorticot ropic Increased adrenocor ticotropic hormone secretion Gonadotr opin- releasing hormone (GnRH) Small peptide Anterior pituitary cells that secrete luteinizing hormone and follicle – stimulating hormone Increased secretion of luteinizin g hormone and follicle- stimulatin g hormone Prolactin
inhibiting hormone Unknown (possibly dopamine ) Anterior pituitary cells that secrete prolactin Decrease d prolactin secretion (PIH) Prolactin
releasing hormone (PRH) Unknown Anterior pituitary cells that secrete prolactin Increased prolactin secretion HORMONES OF THE POSTERIOR PITUITARY GLAND Stores and secretes two polypeptide hormones Antidiuretic hormone (ADH) Promotes water retention by the kidneys Oxytocin Promotes uterine contractions during delivery Causes milk ejection in lactating women HORMONES OF THE PITUITARY Anterior Pituitary Growth hormone (GH) Thyroid – stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH) Melanocyte – stimulating hormone (MSH) Luteinizing hormone (LH) Follicle – stimulating hormone (FSH) Prolactin GROWTH HORMONE GH stimulates growth in most tissues and is a regulator of metabolism GH stimulates The uptake of amino acids and their conversion into proteins The breakdown of fats and the synthesis of glucose the production of somatomedins (with GH they promote bond and cartilage growth) GH secretion increases in response to low blood glucose, stress, and an increase in certain amino acids GH is regulated by two hypothalamic hormones growth hormone – releasing hormone (GHRH) growth hormone – inhibiting hormone (GHIH)
Tetraiodothyronine (thyroxine or T 4 ¿:
has two tyrosine molecules plus four bound iodne atoms (10%) EFFECTS OF THYROID HORMONE
T 3 ∧ T 4
Increased the rate of glucose, fat, and protein metabolism in many tissues Increase body temperature
T 3 ∧ T 4 play arole ∈¿
Maintaining blood pressure Regulating tissue growth Developing skeletal and nervous systems Maturation and reproductive capabilities Goiter Lack of iodine intake Hyperplasia of thyroid cells Enlargement of thyroid gland Exophthalmos in Hyperthyroidism Myxedema in Hypothyroidism Crertinism CALCITONIN Parafollicular cells secrete calcitonin
Directly regulated by blood Ca +^2 levels
Blood Ca +^2 levels drop = calcitonin
levels drop
Blood Ca +^2 levels rise = calcitonin
levels rise Calcitonin targets the skeleton to Inhibit osteoclast activity and the release of calcium from the bone matrix Stimulate calcium uptake and incorporation into the bone matrix PARATHYROID GLAND Tiny glands embedded in the posterior aspect of the thyroid Secrete a polypeptide hormone called parathyroid hormone (PTH) PTH is essential in regulating calcium balance in the blood (much more important than calcitonin)
PARATHYROID HORMONE
PTH increases the release of Ca +^2 from
bones into blood by increasing the number of osteoclasts PARATHYROID GLAND PTH also
Promotes Ca +^2 reabsorption by the
kidneys and the formation of active vitamin D by the kidneys Active vitamin D increases calcium absorption by the intestine
A decrease in blood Ca +^2 levels stimulates
PTH secretion ADRENAL GLANDS Paired, pyramid – shaped organs that sit on top of the kidneys Divided into two parts: Adrenal medulla (inner area) o Arises from the same cells that give rise to postganglionic sympathetic neurons Adrenal cortex (outer area) o Glandular tissue derived from embryonic mesoderm o Composed of three layers Zona glomerulosa Zona fasciculata Zona reticularis Structurally and functionally, they are four glands in one HORMONES OF THE ADRENAL MEDULLA Approximately 80% of the hormones released is epinephrine (adrenaline) and 20% is norepinephrine Secretion of these hormones prepares the body for physical activity by: Increasing blood glucose levels Increasing the use of glycogen and glucose by skeletal muscle Increasing heart rate and force of contraction Causes vasoconstriction in the skin and viscera Causes vasodilation in skeletal and cardiac muscle Released by the sympathetic division of the ANS in response to Emotions Injury Stress Exercise Low blood glucose levels HORMONES OF THE ADRENAL CORTEX Synthesizes and released steroid hormones called corticosteroids Different corticosteroids are produced in each of the three layers
Pancreatic islets (islets of Langerhans) produce hormones (endocrine products) The islets contain two major cell types: Alpha cells that produce glucagon Beta cells that produce insulin INSULIN Target tissues Liver Adipose tissue Muscle Satiety center in the hypothalamus Nervous system relies on blood glucose levels maintained by insulin Increases the uptake of glucose and amino acids by cells Glucose o Is used for energy o Stored as glycogen o Converted into fats Amino acids are used to synthesize proteins Low levels of insulin promote the formation of ketone bodies by the liver GLUCAGON Target tissue is mainly the liver Causes the breakdown of glycogen to glucose Stimulates the synthesis of glucose from amino acids Liver release glucose into the blood PANCREATIC HORMONE SECRETION Insulin Increases because o Elevated blood glucose levels o Increase in some amino acids o Parasympathetic stimulation o Gastrointestinal hormones Sympathetic stimulation decreases insulin secretion Glucagon Secretion is stimulated by o Low blood glucose levels o Certain amino acids o Sympathetic stimulation Somatostatin inhibits insulin and glucagon secretion HORMONAL REGULATION AFTER A MEAL After a meal, the following events take place High glucose levels stimulate insulin secretion but inhibit glucagon, cortisol, GH, and epinephrine secretion Insulin increases the uptake of glucose, amino acids, and fats, which are used for energy or are stored Some hours after the meal, blood glucose levels drop o Insulin levels decrease and glucagon, GH, cortisol, and epinephrine levels increase o Glucose is released from tissues The liver releases glucose into the blood, and the use of glucose by most tissues, other than nervous tissue, decreases Adipose tissue releases fatty acids and ketones, which most tissues use for energy Response to increase Glucagon The liver releases glucose into the blood, and the use of glucose by most tissues, other than nervous tissue, decreases
What happens if glucose is depleted? Adipose tissue releases fatty acids and ketones, which most tissues use for energy HORMONAL REGULATION OF NUTRIENTS During exercise, the following events occur Sympathetic activity increases epinephrine and glucagon secretion, causing a release of glucose from the liver into the blood Low blood sugar levels, caused by the uptake of glucose by skeletal muscles, stimulate epinephrine, glucagon, GH, and cortisol secretion o Causes an increase in fatty acids and ketones in the blood, all of which are used for energy TESTES AND OVARIES Testes Secrete testosterone o Initiates maturation of male reproductive organs o Causes appearance of secondary sexual characteristics and sex drive o Is necessary for sperm production o Maintains sex organs in their functional state Ovaries Secretes estrogens and progesterone o Maturation of the reproductive organs o Appearance of secondary sexual characteristics o Breast development and cyclic changes in the uterine mucosa PINEAL GLAND Small, pinecone-shaped structure located superior and posterior to the thalamus Secretory product is melatonin Melatonin Can inhibit reproductive maturation May regulate Circadian cycle (sleep wake cycles)
1. Light entering the eye stimulates neurons in the retina of the eye to produce action potentials. 2. Action potentials are transmitted to the hypothalamus in the brain 3. Action potentials from the hypothalamus are transmitted through the sympathetic division to the pineal body 4. A decrease in light (dark) results in increased sympathetic stimulation of the pineal glands and increased melatonin secretion. An increase in light results in decreased sympathetic stimulation of the pineal gland and decreased melatonin secretion 5. Melatonin inhibits GnRH secretion from the hypothalamus and may help regulate sleep cycles THYMUS GLAND Lobulated gland located deep to the sternum Major hormonal products are thymopoietin and thymosin These hormones are essential for the development of the T lymphocytes (T cells) of the immune system Disappears in adult years MAJOR ENDOCRINE GLANDS AND THEIR HORMONES Thyroid Gland Thyroid Follicles Thyroid Hormones (T3 and T4) Structure : Amino acid derivative Target tissue : most cells of the body Response: increased metabolic rate; essential for normal process of growth and maturation
Progesterone Structure : steroid Target tissue: most cells Response: uterine and mammary gland development and function; maturation of genitalia; secondary sex characteristics; menstrual cycle Pineal Body Melatonin Structure : amino acid derivative Target tissue: at least the hypothalamus Response: inhibition of gonadotropin – releasing hormone secretion, thereby inhibiting reproduction; significance is not clear in humans; may help regulate sleep – wake cycles Thymus Thymosin Structure : peptide Target tissue: immune tissues Response: development and function of the immune system OTHER ENDOCRINE ORGANS Gastrointestinal tract Produces gastrin, secretin, and cholecystokinin, which regulate digestive functions Kidneys Produce erythropoietin, which stimulates red blood cell production Placenta Secretes human chronic gonadotropin, which is essential for the maintenance of pregnancy HORMONE-LIKE SUBSTANCES Autocrine agents Chemical signals that locally affect cells of the same type as the cell producing the autocrine agent Prostaglandins, thromboxane’s, prostacyclin’s, and leukotrienes Paracrine agents Chemical signals that locally affect cells of a different type than the cell producing the paracrine agent Growth factors, clotting factors, and histamine Autocrine and paracrine chemical signals differ from hormones in that They are not secreted from discrete endocrine glands They have local effects rather than systemic effects They have functions that are not understood in all cases EFFECTS OF AGING ON THE ENDOCRINE SYSTEM There is a gradual decrease in the secretion rate of most, but not all, hormones Some decreases are secondary to gradual decreases in physical activity SYSTEMS INTERACTIONS
