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BIOB32H3 Lecture Notes - Thymus, Adrenal Medulla, Pars Tuberalis

Biological Sciences
Course Code
Kenneth Welch

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The Endocrine System
Intercellular Communication
Endocrine versus Nervous system
Nervous system performs short term crisis management
Endocrine system regulates long term ongoing metabolic
Endocrine communication is carried out by endocrine cells releasing hormones
Alter metabolic activities of tissues and organs
Target cells
Paracrine communication involves chemical messengers between cells within one
An Overview of the Endocrine System
Endocrine system
Includes all cells and endocrine tissues that produce hormones or paracrine factors
Hormone structure
Amino acid derivatives
Structurally similar to amino acids
Peptide hormones
Chains of amino acids
Lipid derivatives
Steroid hormones and eicosanoids
Hormones can be
Freely circulating
Rapidly removed from bloodstream
Bound to transport proteins
Mechanisms of hormone action
Receptors for catecholamines, peptide hormones, eicosanoids are in the cell
membranes of target cells
Thyroid and steroid hormones cross the membrane and bind to receptors in the
cytoplasm or nucleus
Control of endocrine activity
Endocrine reflexes are the counterparts of neural reflexes
Hypothalamus regulates the activity of the nervous and endocrine systems
Secreting regulatory hormones that control the anterior pituitary gland
Releasing hormones at the posterior pituitary gland
Exerts direct neural control over the endocrine cells of the adrenal medullae
Endocrine System
The Pituitary Gland
Releases nine important peptide hormones

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All nine bind to membrane receptors and use cyclic AMP as a second messenger
The anterior lobe (adenohypophysis)
Subdivided into the pars distalis, pars intermedia and pars tuberalis
At the median eminence, neurons release regulatory factors through fenestrated
Releasing hormones
Inhibiting hormones
The Endocrine System
Hypophyseal portal system
All blood entering the portal system will reach the intended target cells before
returning to the general circulation
Hormones of the adenohypophysis
Thyroid stimulating hormone (TSH)
Triggers the release of thyroid hormones
Thyrotropin releasing hormone promotes the release of TSH
Adrenocorticotropic hormone (ACTH)
Stimulates the release of glucocorticoids by the adrenal gland
Corticotrophin releasing hormone causes the secretion of ACTH
Hormones of the adenohypophysis
Follicle stimulating hormone (FSH)
Stimulates follicle development and estrogen secretion in females and sperm
production in males
Leutinizing hormone (LH)
Causes ovulation and progestin production in females and androgen production
in males
Gonadotropin releasing hormone (GNRH) promotes the secretion of FSH and LH
Hormones of the adenohypophysis
Prolactin (PH)
Stimulates the development of mammary glands and milk production
Growth hormone (GH or somatotropin)
Stimulates cell growth and replication through release of somatomedins or IGF
Growth-hormone releasing hormone
Growth-hormone inhibiting hormone
Melanocyte stimulating hormone (MSH)
May be secreted by the pars intermedia during fetal development, early childhood,
pregnancy or certain diseases
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