ENDOCRINE SYSTEM AND BEHAVIOR

 ENDOCRINE SYSTEM AND BEHAVIOR

Types of chemical messenger systems:

 

1. Neurotransmitters - are released by axon terminals of neurons into the synaptic junctions and act locally to control nerve cell functions.

2. Endocrine hormones - are released by glands or specialized cells into the circulating blood and influence the function of target cells at another location in the body.

3. Neuroendocrine hormones-  are secreted by neurons into the circulating blood and influence the function of target cells at another location in the body

4. Paracrines- Cells produce paracrines into the extracellular fluid, which have an effect on surrounding target cells of a different type.

5. Autocrines- Autocrines are secreted into the extracellular space by cells. fluid and have an impact on the function of the same cells that they were created

6. Cytokines are peptides secreted by cells into the extracellular fluid

 

Endocrine Hormones-The circulatory system transports endocrine hormones to cells all over the body, including the nervous system in some situations, where they connect to receptors and trigger a variety of cell reactions. Endocrine hormones have a wide range of effects on the body's cells.Other hormones primarily influence certain target tissues, which have a large number of receptors for the hormone.The multiple hormone systems play a key role in regulating almost all body functions, including metabolism, growth and development, water and electrolyte balance,reproduction, and behavior.

 

Gland	Hormone	Functions
Hypothalamus	1. Thyrotropin-releasing hormone 2. Corticotropin-releasing hormone 3. Growth hormone–releasing hormone 4. Growth hormone inhibitory hormone (somatostatin) 5. Gonadotropin-releasing hormone 6. Dopamine or prolactin-inhibiting factor	1. Thyroid-stimulating hormone and prolactin release are stimulated. 2. stimulates release of adreno-cortico-tropic hormone 3. stimulates release of growth hormone   4. Inhibits release of growth hormone     5.Causes release of luteinizing hormone and follicle-stimulating hormone 6. Inhibits release of prolactin
Anterior pituitary	1. Growth hormone 2.Thyroid stimulating hormone   3.Adrenocorticotropic hormone   4.Prolactin   5.Follicle-stimulating hormone   6.Luteinizing hormone	1.Stimulates protein synthesis and overall 2.Stimulates synthesis and secretion of thyroid hormones 3.Stimulates synthesis and secretion of adrenocortical hormones 4.Promotes development of the female breasts and secretion of milk 5.Causes growth of follicles in the ovaries and Sperm 6.Stimulates testosterone synthesis, stimulates ovulation,and estrogen and progesterone synthesis in ovaries
Posterior pituitary	1.Antidiuretic hormone   2.Oxytocin	1.Increases water re-absorption by the kidneys 2.Stimulates milk ejection from breasts and uterine contractions
Thyroid	1.Thyroxine (T4) and triiodothyronine (T3)   2.Calcitonin	1.Increases the rates of chemical reactions in most cells, thus increasing body metabolic rate 2.Promotes deposition of calcium in the bones
Adrenal cortex	1.Cortisol AKA Stress hormone 2.Aldosterone	1.Has multiple metabolic functions   2.Increases renal sodium reabsorption, potassium secretion
Adrenal medulla	1.Norepinephrine and epinephrine	1.Sympathetic/parasympathetic stimulation
Pancreas	1.Insulin (beta cells) 2.Glucagon (α cells)	1.controls carbohydrate metabolism 2.Increases synthesis and release of glucose from the liver into the body fluids
Parathyroid	1.Parathyroid hormone	1.Controls serum calcium ion concentration
Testes	1.Testosterone	1.Promotes development of male reproductive system and male secondary sexual characteristics
Ovaries	1.Estrogens   2.Progesterone	1.Promotes growth and development of female reproductive system 2.Stimulates secretion of “uterine milk” by the uterine endometrial glands

 

 

FEEDBACK CONTROL OF HORMONE SECRETION

 

Negative Feedback Mechanism-Although several hormones' plasma concentrations fluctuate in response to diverse stimuli throughout the day, all hormones appear to be strictly controlled. Most of the time, this control is achieved by negative feedback mechanisms that maintain a suitable amount of hormone activity in the target tissue.Conditions or products resulting from the hormone's action tend to suppress its further release . To put it another way, the hormone (or one of its derivatives) has a negative feedback effect that keeps oversecretion at check.

 

Positive Feedback Mechanism-Positive feedback happens in a few circumstances when the hormone's biological function causes it to secrete more hormone. The surge of luteinizing hormone (LH) that occurs as a result of estrogen's stimulatory impact on the anterior pituitary before ovulation is an example of positive feedback. The secreted LH then acts on the ovaries, causing more oestrogen to be released, which in turn causes more LH to be secreted.

 

Cyclic Variations- Periodic fluctuations in hormone release, driven by seasonal changes, distinct phases of growth and ageing, the diurnal cycle, and sleep, are superimposed on the negative and positive feedback control of hormone secretion.

Pituitary Hormones and Their Control by the Hypothalamus

 

The pituitary gland also called the hypophysis, is a small gland.The pituitary (or hypophysial) stalk connects the pituitary gland to the hypothalamus. The anterior pituitary, also known as the adenohypophysis, and the posterior pituitary, sometimes known as the neurohypophysis, are two different sections of the pituitary gland. The pars intermedia is a tiny, avascular zone that lies between these two sections.

The anterior pituitary secretes six major peptide hormones as well as several other lesser-known hormones, while the posterior pituitary secretes two key

peptide hormones.

 

Anterior Pituitary-Several different cell types synthesise and secrete hormones in the anterior pituitary gland. In the anterior pituitary gland, each main hormone is usually generated by a single cell type.These five cell types are as follows:

1. Somatotropes—human growth hormone (hGH)

2. Corticotropes—adrenocorticotropic hormone (ACTH)

3. Thyrotropes—thyroid-stimulating hormone (TSH)

4. Gonadotropes—gonadotropic hormones, which include both luteinizing hormone (LH) and follicle-stimulating hormone (FSH)

5. Lactotropes—prolactin (PRL)

 

Posterior Pituitary- The bodies of the cells that secrete posterior pituitary hormones are enormous neurons called magnocellular neurons that are found in the supraoptic and paraventricular areas of the brain.The hormones are then transported in the axoplasm of the neuron’s nerve fibers passing from the hypothalamus to the posterior pituitary gland.

 

HYPOTHALAMUS CONTROL-Nerve impulses that begin in the hypothalamus and terminate in the posterior pituitary govern secretion from the posterior pituitary. In contrast, hormones called hypothalamic releasing and hypothalamic inhibitory hormones (or factors) released within the hypothalamus and then carried to the anterior pituitary by minute blood channels called hypothalamic-hypophysial portal vessels govern secretion by the anterior pituitary. These releasing and inhibiting hormones act on the glandular cells in the anterior pituitary to regulate their output.

The major hypothalamic releasing and inhibitory hormones are:

1. Thyrotropin-releasing hormone (TRH), which causes release of TSH

2. Corticotropin-releasing hormone (CRH), which causes release of ACTH

3. Growth hormone–releasing hormone (GHRH), which causes release of GH, and growth hormone inhibitory hormone (GHIH), also called somatostatin, which inhibits release of GH

4. Gonadotropin-releasing hormone (GnRH), which causes release of the two gonadotropic hormones, LH and FSH

5. Prolactin inhibitory hormone (PIH), also known as dopamine, which causes inhibition of prolactin secretion

 

ABNORMALITIES OF HORMONES:

 

1. Growth Hormone-Panhypopituitarism—Decreased Secretion of All Anterior

 

2.Pituitary Hormones,Panhypopituitarism in the Adult,Panhypopituitarism During Childhood and Dwarfism, Acromegaly and Excess Growth Hormone After Adolescence.

 

3.Thyroid-Hyperthyroidism,Toxic Goiter, Thyrotoxicosis, Graves’ Disease,Thyroid Adenoma,Hypothyroidism,Cretinism

 

4.Adrenocortical Secretion-Addison’s Disease,Melanin Pigmentation.,Cushing’s Syndrome,Conn’s Syndrome

 

5..Insulin, Glucagon-Diabetes Mellitus,Insulinoma—Hyperinsulinism,