Coordinated functions Nervous systemEndocrinal system Control system
Control systems vary in their speed & specificity – Specificity Nervous control very specific Hormonal control more general – Nature of signal Nervous system uses both electrical and chemical Endocrine system uses only chemicals – Speed Nervous system much faster, up to 120 m/sec Endocrine system much slower – Duration of action Nervous system shorter, very brief Endocrine system lasts longer
Coordinating multiple activities of the cell, tissues and organs of the body. Maintain homeostasis Regulating almost all body functions. Chemical messenger system
Classic definition- hormones are secretory product of the ductless glands, which are released in catalytic amount into blood stream and transported to specific target cells(or organs),where they elicit physiological, morphological and biochemical responses. hormone "to set in motion,"
What is the Endocrine System? Mutiple hormone system controls numerous body processes Numerous organs and tissues located throughout the body Works in conjunction with the nervous system growth and development metabolism reproduction behavior Water and electrolyte balance homeostasis Regulating all most all body functions
Act to evoke or suppress hormone secretion in response to both external and internal stimuli. External stimuli- visual, auditory, olfactory, gustatory and tactile Internal stimuli- pain, emotion, stress, fright, change in blood volume 2. Neural control
Oscillating and pulsatile release of certain hormones Diurnal variation in hormonal levels Menstural rhythm Seasonal rhythm Developmental rhythm 3. Chronotropic control
Objectives After the end of this lecture a student should be able to Name the hypothalamic hormones that regulate anterior pituitary function. Explain hypothalamo – hypophyseal portal system Name the hormones that are released from anterior pituitary Name the hormones that are released from posterior pituitary Explain the functions of pituitary hormones
Hypothalamus and Pituitary The hypothalamus-pituitary unit is the most dominant portion of the entire endocrine system. The output of the hypothalamus-pituitary unit regulates the function of the thyroid, adrenal and reproductive glands and also controls somatic growth, lactation, milk secretion and water metabolism. Pituitary function depends on the hypothalamus and the anatomical organization of the hypothalamus-pituitary unit reflects this relationship.
Reituclar activating substance Thalamus neocortex Limbic system Optical system Heat regulation (temperature) Energy regulation (hunger, BMI) Autonomic regulation (blood pressure etc) Water balance (blood volume, intake--thirst, output—urine volume) Metabolic rate, stress response, growth, reproduction, lactation) Sleep/ wake pain Emotion, fright, rage, smell vision Anterior pituitary hormones posterior pituitary hormones Regulation of Hypothalamus
Releasing Hormones secreted by hypothalamic neurons and transported to the anterior pituitary by the hypothalamic-hypophyseal portal system function as trophic hormones to either stimulate or inhibit release of anterior pituitary hormones
endocrine axes have the following important features 1.The activity of a specific axis is normally maintained at a set point, which varies from individual to individual, usually within a normal range. 2.Hypothalamic hypophysiotropic neurons are often secreted in a pulsatile manner and are entrained to daily and seasonal rhythms through CNS input 3.Abnormally low or high levels of a peripheral hormone (e.g., thyroid hormone) may be due to a defect at the level of the peripheral endocrine gland (e.g., thyroid), the pituitary gland, or the hypothalamus. Such lesions are referred to as primary, secondary, and tertiary endocrine disorders, respectively.
The Lactotrope The lactotrope is not part of an endocrine axis. This means that PRL acts directly on nonendocrine cells (primarily of the breast) to induce physiological changes. Production and secretion of PRL are predominantly under inhibitory control by the hypothalamus. Thus, disruption of the pituitary stalk and the hypothalamohypophysial portal vessels (e.g., secondary to surgery or physical trauma) results in an increase in PRL levels but a decrease in ACTH, TSH, FSH, LH, and GH.
FSH and LH GHRH CRH TRHPIHSS Anterior Pituitary GROWTH HORMONE TSH PROLACTIN ACTH Hypothalamus GnRH Hormones-estrogen, progesterone and testosterone Other organs IGF-1 Gonads Adrena l cortex Liver ThyroidBreasts Growth Metabolism Germ cell development Development Milk Cortisol Thyroxine T3 Summary of Hypothalamic-anterior-pituitary system
Action of Growth Hormone 1.stimulates growth of bone, cartilage & connective tissue through somatomedins & other growth factors. 2.Growth Hormone Promotes Protein deposition in Tissues. 3. Growth Hormone Enhances Fat Utilization for Energy. 4.Growth Hormone Decreases Carbohydrate Utilization
Hypothalamic Control of Posterior Pituitary Hypothalamic neuron cell bodies produce: ADH: supraoptic nuclei. Oxytocin: para ventricular nuclei. Transported along hypothalamo-hypophyseal tract. Stored in posterior pituitary. Release controlled by neuroendocrine reflexes.
ACTIONS OF ADH 1.ACTION ON KIDNEY Maintenance of ECF volume & Osmolarity Acts on DCT and CD of kidney Reabsorbs water Maintenance of volume more important that maintenance of osmolarity 2.VASOCONSTRICTOR EFFECT 3.ACTION ON ANTERIOR PITUITARY-cause increased ACTH secretion from the corticotroph
Actions of oxytocin In females: Milk ejection Contraction of uterus during labor In females: during coitus causes uterine contraction and transport of sperms In Males: Increases at time of ejaculation May cause increase contraction of smooth muscle of vas deferens - propelling sperm through urethra
IN THE CLINIC-- hypophysectomy (pituitary removal) Because posterior pituitary hormones are synthesized in the hypothalamus rather than the pituitary, hypophysectomy (pituitary removal) does not necessarily permanently disrupt synthesis and secretion of these hormones. Immediately after hypophysectomy, secretion of the hormones decreases. However, over a period of weeks, the severed proximal end of the tract will show histological modification and pituicytes will form around the neuron terminals. Secretory vacuoles are seen, and secretion of hormone resumes from this proximal end. Secretion of hormone can even potentially return to normal levels. In contrast, a lesion higher up on the pituitary stalk can lead to loss of neuronal cell bodies in the PVN and SON.
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