Clinical Chemistry 2: Intro to Endocrinology, Pituitary & Hormones PDF

LESSON 13: Intro to Endocrinology, Pituitary and Hormones Why is the Endocrine System Important? LECTURER: Dr. Marie Angela Nee C. MAINTENANCE OF HOMEOSTASIS & REGULATION OF...

LESSON 13: Intro to Endocrinology, Pituitary and Hormones Why is the Endocrine System Important? LECTURER: Dr. Marie Angela Nee C. MAINTENANCE OF HOMEOSTASIS & REGULATION OF BODILY PROCESSES INTRODUCTION TO ENDOCRINOLOGY (HYPOTHALAMIC & PITUITARY FUNCTION) A. ENDOCRINOLOGY Branch of medicine that specializes in diagnosing and treating disorders of the endocrine system, which includes ○ The glands and organs that make hormones. These disorders include diseases like: ○ Diabetes, infertility, and thyroid, adrenal, and pituitary gland problems. B. INTRACELLULAR COMMUNICATION BY CHEMICAL MESSENGERS Use of neurotransmitters which are NEURAL released at synaptic junctions and act locally. Uses hormones released from specialized glands or cells, which reach the circulating blood and influence the function of target cells some distance away. Examples of hormones: ENDOCRINE ○ Prolactin Secreted by pituitary gland. Neuroendocrine System Has an effect on the breast in Control of body processes is achieved through interactions instances when a woman is between neural and endocrine systems. breastfeeding. Linked by neuroendocrine cells (and the neuroendocrine [This is the topic for this lecture] system) located at the hypothalamus whose axons Secretion/Secreted products from terminate in the posterior pituitary gland and median neurons (neurohormones) reach the eminence. circulating blood and influence the ○ Antidiuretic Hormone (ADH) function of target cells some distance ○ Oxytocin away. ○ Hypophysiotropic Hormones NEURO- Control secretion of the anterior pituitary hormone. ENDOCRINE LECTURER’S NOTES: The main difference between LECTURER’S NOTES (regarding parts of the image above): Endocrine and Neuroendocrine is Our neuroendocrine cells include: that the latter uses products from 1. Supraoptic Nucleus neurons instead of glands. In the hypothalamus. 2. Paraventricular Nucleus Cell secretion products diffuse into the 3. Magnocellular Neuron PARACRINE extracellular fluid and affect Both (2) and (3) are connected to the Pituitary neighboring target cells. Gland by synaptic connections. Cell secretion products affect the SYNAPTIC CONNECTIONS function of the same cell by binding to AUTOCRINE The synaptic connections terminate either the: cell surface receptors. ○ Same cell that is secreting it. ○ Posterior Pituitary Gland ○ Median Eminence The secretions could be released here. It contains blood vessels which, in turn, carry the hormones into the Anterior Pituitary Gland. II. HORMONES Hormones can be made up by: Peptides from as small as three amino Proteins and acids (thyrotropin-releasing hormone) to Peptides proteins almost 200 amino acids long (growth hormone and prolactin.) Derivatives of cholesterol and includes: 1. Adrenocortical Hormones Steroids ○ (cortisol, aldosterone) 2. Gonadal Hormones ○ (testosterone, estrogen, progesterone) This transcript is strictly confidential and is intended for AVR 5TH FLOOR group members only; please don’t share or distribute! 1  CLINICAL CHEMISTRY 2 | Lesson 13: Intro to Endocrinology, Pituitary and Hormones 1. Hormones from the Thyroid Gland. POSTERIOR Derivatives of Derived from downgrowth of cells ○ (Thyroxine, Triiodothyronine) PITUITARY GLAND/ the amino acid from the third ventricle of the brain. 2. Hormones from the Adrenal Medulla. NEUROHYPOPHYSIS TYROSINE ○ (Epinephrine, Norepinephrine) Pituitary gland is connected to the hypothalamus by the hypothalamic or pituitary stock. A. CONTROL OF HORMONAL SECRETION Controlled by the negative feedback loop. ○ Endocrine at baseline they tend to over secrete the hormone to drive target cell function. ○ When too much function of the target cells occurs, there is a negative feedback to the endocrine gland. ○ Signals the endocrine gland to stop producing the hormone. ○ Negative effect on the gland, decreasing its secretory rate. Pituitary stock. EXAMPLE IV. POSTERIOR PITUITARY GLAND/ NEUROHYPOPHYSIS Simple feedback loop. Pituitary gland Hypothalamus which produces your TRH (thyrotropin Posterior pituitary — stores hormones synthesized in the 1 releasing hormone) that stimulates the pituitary gland to hypothalamus. produce your thyroid stimulating hormone (TSH). ○ Pituitary gland actually does not synthesize hormones. In turn, your TSH will then stimulate your thyroid gland to 2 produce thyroxine. MAGNOCELLULAR NEURONS- Posterior pituitary gland An increased amount of thyroxine inside the body would Whose cell bodies are located in the hypothalamus 3 eventually stimulate your hypothalamus to STOP synthesize the neurohypophysial hormones. producing TRH. Location: extends to the posterior lobe of the pituitary gland Therefore, without the action of TRH, the pituitary gland Antidiuretic hormone (ADH) and oxytocin. 4 TSH would also be decreased and then the thyroid would ○ Two hormones which are stored in the pituitary gland. also STOP producing thyroid hormones or thyroxine. SECRETION GRANULES CONTAINING NEUROHORMONES B. ACTIVATION OF HORMONAL RECEPTORS They are transported from the cell bodies in the Control cellular processes by interacting with receptors on hypothalamus → axons in the pituitary stalk → storage target cells. sites in nerve terminals located in the posterior pituitary THE RECEPTORS LOCATION gland. ADH and oxytocin are released from secretion granules into On or within Cell which peptide or protein hormones the capillary plexus of the inferior hypophysial artery. Membrane and catecholamine hormones use. Within the cell or A. OXYTOCIN & ADH/AVP either in the such as the target organs or cells for cytoplasm or steroid and thyroid hormones. nucleus III. PITUITARY HORMONES A. PITUITARY GLAND AKA master/ gland of the endocrine system. DIVIDED INTO 2 PORTIONS ANTERIOR Derived embryologically from an PITUITARY GLAND/ upward invagination of cells from ADENOHYPOPHYSIS the oral cavity (Rathke's Pouch). Cell Bodies of Magnocellular Neurons This transcript is strictly confidential and is intended for AVR 5TH FLOOR group members only; please don’t share or distribute! 2  CLINICAL CHEMISTRY 2 | Lesson 13: Intro to Endocrinology, Pituitary and Hormones SYNTHESIZED AS PREPROHORMONES Initiated by: Receptors on the nipples of the breast. In the cell bodies of magnocellular neurons located in the ○ When a baby starts to suckle, it sends a signal — an supraoptic and paraventricular nuclei. Ascending Sensory Information — to the Preprohormones (inactive) need to be activated by hypothalamus of the brain. removing a certain protein for it to become a prohormone. Prohormone has to be activated into an active hormone SUCKLING STIMULATION BRINGS ABOUT: Originally, when they are synthesized in the Hypothalamus, 1 OXYTOCIN - POSTERIOR Pituitary they are still inactive - thus, they are preprohormones. The suckling will bring about reflex stimulation of ○ When they are inactive, they are still bound to oxytocin-containing neuroendocrine cells. neurophysin. ○ And the section of oxytocin from the Posterior ○ They then travel down the axon into the Posterior Pituitary Gland. Pituitary Gland, where they can be activated. The release of oxytocin causes smooth muscle contraction. Synthesized largely in the ○ Thus, there will be more milk secretion. OXYTOCIN paraventricular nucleus 2 INHIBITION OF PIH - ANTERIOR Pituitary Green Cells in the pic above The suckling will also bring about the inhibition of Synthesized largely in the supraoptic Prolactin-Inhibiting Hormone (PIH) in the Anterior ADH nucleus Pituitary. Purple Cells in the pic above ○ With the inhibition of PIH, the Anterior Pituitary Gland Part of the preprohormone. will produce Prolactin. The protein attached to ADH and ○ Thus, there will be more milk secretion. NEUROPHYSIN oxytocin while in the hypothalamus, so that they remain inactive. LECTURER’S NOTES: A mother of a newborn who complains about not being B. OXYTOCIN able to produce enough milk is usually advised to just continue trying to breastfeed the baby. ○ This is to keep stimulating the Milk Ejection Reflex so they will eventually be able to produce more milk. ○ Also so that the myoepithelial cells are able to contract and excrete the milk that is stored in the alveoli. C. ANTIDIURETIC HORMONE (ADH)/ ARGININE VASOPRESSIN (AVP) Regulates the osmolality of body fluids by altering renal excretion of water. ○ Sensitive to changes in plasma osmolality. ○ Even a 1% change in plasma osmolality can cause the Milk Ejection Reflex secretion of ADH. Plays an important role in lactation by causing milk ejection. ADH secretion is regulated by osmoreceptors in the ○ This is also known as the Let Down Reflex, or the Milk Anterior hypothalamus that send nervous signals to the Reflex. supraoptic and paraventricular nuclei. Oxytocin’s action causes contraction of the myoepithelial cells of the alveoli of the mammary glands. EFFECTS OF ADH ○ This forces milk from the alveoli into the ducts so the 1 ABSENCE OF ADH - Less water reabsorption. baby can obtain it by suckling. In the absence of ADH, the collecting tubules and collecting ducts are largely impermeable to water. MILK EJECTION REFLEX - Oxytocin ○ This prevents significant reabsorption of water in this portion of the nephron. 2 INCREASE ↑ OF ADH - More water reabsorption. Increased ADH activates V2-receptors of the kidneys, on the basolateral side of the tubules via a cyclic-AMP (cAMP) second messenger system. ○ Once the V2 Receptors are activated by ADH: Cytoplasmic vesicles containing aquaporin are inserted in the apical membrane. Thus, increases the permeability of the tubules to water. MIlk Ejection Reflex This transcript is strictly confidential and is intended for AVR 5TH FLOOR group members only; please don’t share or distribute! 3  CLINICAL CHEMISTRY 2 | Lesson 13: Intro to Endocrinology, Pituitary and Hormones DIAGRAM OF ADH Drugs ○ Morphine ○ Nicotine ○ Barbiturates Hypervolemia ○ Correct fluid status of body. Hypertension ○ Excrete more water; decrease blood volume. DECREASE ↓ADH Alcohol ○ Drinking alcoholic beverages makes you urinate large portions of ADH dilute urine often since alcohol inhibits ADH secretion. LOW secretion of ADH Aquaporin C1. DISEASES CAUSED BY AN ABNORMALITY OF ADH ○ channels in which water is reabsorbed. C1.1 SYNDROME OF INAPPROPRIATE ANTIDIURETIC WELL ○ FEW in the basolateral membrane HORMONE (SIADH) HYDRATED and the rest will stay WITHIN the cell. A disease which is caused by an abnormal increase of the ○ In this way we only have a few antidiuretic hormone. receptors for water to be reabsorbed, Inappropriate hypersecretion of ADH either from its: so only MINIMAL water is reabsorbed back into the bloodstream. NORMAL HYPOTHALAMIC Caused by tumor or head trauma SOURCE HIGH secretion of ADH ECTOPIC Cancer cells producing ADH Aquaporin PRODUCTION abnormally ○ Travel INTO the basolateral DEHYDRATED membrane of the collecting tubules, CAUSES OF SIADH CAN BE DIVIDED INTO: causing an INCREASE in the water 1 Nervous system disorders that is reabsorbed. 2 Neoplasia 3 Pulmonary diseases ADH/AVP in Maintenance of Blood Pressure 4 Drug-induced Contributes to the maintenance of blood pressure during hypovolemia. SIADH PRESENTS WITH: Stimulation of ADH secretion by hypovolemia and/or 1 Hyponatremia hypotension is achieved by reflexes initiated from receptors Inappropriately ↑elevated urine osmolality (>100 2 in the carotid sinus and aortic arch (high pressure) and mOsm/kg) atria (low pressure). 3 ↓Decreased serum osmolality in a euvolemic patient Receptors that can Detect Change in Pressure High Pressure Carotid sinus and aortic arch Low Pressure Atria At least a 5% decrease in blood volume is necessary to increase ADH secretion. ADH constricts vascular smooth muscle and helps restore blood pressure to normal levels. ○ Result of the ADH peptide binding to vascular V1-receptors on arteriolar smooth muscle. Summarized causes of ADH - SIADH LECTURER’S NOTES: CAUSES OF ADH – SIADH V2-receptors- reabsorption of water in the kidneys 1 Paraneoplastic Syndrome V1-receptors- constriction of blood vessels Tumor outside the brain which secretes ADH. Most commonly caused by small cell lung carcinoma. ADH SECRETION 2 Pneumonia ADH secretion is influenced by multiple factors. 3 Chronic Obstructive Pulmonary Disease (COPD) 4 Surgeries of CNS OTHER FACTORS THAT STIMULATE OR DECREASE ADH 5 Head Trauma SECRETION Damages pituitary Hypovolemia ○ The pituitary gland is damaged so the stored ADH is Hypotensions released into the bloodstream. INCREASE↑ADH Nausea Pain C1.2. DIABETES INSIPIDUS Stress Defined as the passage of large volumes (>3L/24hr) of dilute urine (