Endocrine System

Harliansyah Dept Biochemistry

University of YARSI

Hormones are chemical substances, involved in cell to cell communication, that promote the maintenance of homeostasis. Hormones are blood borne substances involved in regulating a variety of processes. The word ‘ hormone’ is derived from the Greek hormaein which means to excite or to stir up. The endocrinology is the branch of physiology concerned with the description and characterization of processes involved in the regulation and integration of cells and organ systems. The Endocrine System forms an important communication system that serves to Regulate, Integrate and Coordinate a variety of different physiological processes The process that hormones regulate fall into four areas: 1.  The digestion, utilization and storage of nutrient 2.  Growth and development 3. Ion and water balance 4. Reproductive function

General Characteristics •  Glands that secrete chemical

signals (hormones) into circulatory system

•  Hormone characteristics –  Produced in small

quantities –  Secreted into intercellular

space –  Transported some

distance in circulatory system

–  Acts on target tissues elsewhere in body

•  Regulate activities of body structures

•  Ligands: more general term for chemical signals

4 Classes of Hormones

1.  Peptide/ Protein 2.  Steroid 3.  Amine 4.  Eicosanoid

Protein/Peptide Hormones

•  Hydrophilic •  Large •  Can't fit through membrane •  Second messenger mechanism of action •  Most hormones •  Example: Insulin

Steroid Hormones

•  Small •  Hydrophobic/Lipophilic •  Travel in blood w/carrier •  Cytoplasmic or nuclear receptors •  change protein synthesis •  Example: estradiol

Amine

•  Synthesized from a single amino acid

•  Melatonin from tryptophan •  Thyroid hormone from tyrosine •  Catecholamines (EPI, DA) from

tyrosine

Eicosanoid

•  Produced from 20-carbon fatty acid, arachadonic acid

•  Produced in all cells except RBCs

•  2nd messenger •  Prostaglandins and leukotrienes •  inflammation

Hormone + Receptor

•  Steroid •  Hormone •  Mechanism

Regulation of Activities:

Comparison of Endocrine and

Nervous Systems

•  Endocrine: amplitude modulated signals. –  Amount of hormone determines

strength of signal –  Onset within minutes of secretion of

hormone •  Nervous: frequency-modulated

signals. –  Frequency of action potentials

produced by neurons determines strength of signal.

–  Onset within milliseconds •  Two systems actually inseparable

–  Nervous system secretes neurohormones into circulatory system

–  Nervous system uses neurotransmitters and neuromodulators as ligands

–  Some parts of endocrine system innervated directly by nervous system

Intercellular Chemical Signals

•  Hormones: type of intercellular signal. Produced by cells of endocrine glands, enter circulatory system, and affect distant cells; e.g., estrogen

•  Autocrine: released by cells and have a local effect on same cell type from which chemical signals released; e.g., prostaglandin

•  Paracrine: released by cells and affect other cell types locally without being transported in blood; e.g., somatostatin

•  Pheromones: secreted into environment and modify behavior and physiology; e.g., sex pheromones

•  Neurohormone: produced by neurons and function like hormones; e.g., oxytocin

•  Neurotransmitter or neuromodulator: produced by neurons and secreted into extracellular spaces by presynaptic nerve terminals; travels short distances; influences postsynaptic cells; e.g., acetylcholine.

Hypothalamus

GRH TRH CRH Dopamine PRF, PIF GnRH

GH TSH ACTH LPH β-Endorphin PRL FSH LH MSH

Anterior pituitary

Growth of bone, body tissues; carbohydrate

and protein metabolism;

production of IGFs

Hyperglycemic effects

Thyroid hormones

Liver Thyroid Adrenal cortex Mammary gland Ovary

Testis

Corticosteroids

β-Endorphin

Analgesia

Skin darkening Testis

Cell development,

lactation

Development of follicles, estradiol

Growth of seminal tubules and

spermatogenesis

Ovary

Ovulation, corpus luteum, progesterone

Interstitial cell development, testosterone

GH-Growth hormone, TSH-Thyrotropin, ACTH-Adrenocorticotropic hormone, LPH-Lipotropin, MSH-Melanocyte stimulating hormone, PRL-Prolactin, FSH-Follicle stimulating hormone, LH-Luteinizing hormone

CNS

Limbic system

Hypothalamus

Anterior pituitary

Adrenal gland

Environmental stress

A single stressor (change in temperature, noise, trauma) Electrical-chemical signal

Electrical-chemical signal

Corticotropin releasing hormone (CRH) in ng, t1/2 minutes

Adrenocorticotropic hormone (ACTH) in µg, increased t1/2

Cortisol in mg, t1/2 hours

The glucocorticoid receptors in different cells

Portal system

The corticotrophic cells

Systemic effects

CRH-ACTH-Cortisol

CNS

Limbic system

Hypothalamus

Anterior pituitary

Target „gland“

Environmental or internal signal

Electrical-chemical signal

Electrical-chemical signal

Releasing hormones (ng)

Anterior pituitary hormone (µg)

Ultimate hormone (mg)

Systemic effects

The gonads, the thyroid gland, the adrenal cortex

Hormonal cascade Signal amplification

CNS

Limbic system

Hypothalamus

Anterior pituitary

Target „gland“

Releasing hormones

Anterior pituitary hormones

Ultimate hormone

Systemic effects

Short feedback loop

Long feedback loop

Hormonal cascade Negative feedback system

Control Pathways and Feedback Loops

•  There are three types of hormonal control pathways

Pathway Example

Stimulus Low blood glucose

Receptor protein

Pancreas secretes glucagon ( )

Endocrine cell Blood

vessel

Liver Target

effectors

Response

Pathway Example

Stimulus Suckling

Sensory neuron

Hypothalamus/ posterior pituitary

Neurosecretory cell

Blood vessel

Posterior pituitary secretes oxytocin ( )

Target effectors

Smooth muscle in breast

Response Milk release

Pathway Example

Stimulus Hypothalamic neurohormone released in response to neural and hormonal signals

Sensory neuron

Hypothalamus secretes prolactin- releasing hormone ( )

Neurosecretory cell

Blood vessel

Anterior pituitary secretes prolactin ( ) Endocrine

cell Blood vessel

Target effectors

Response

Mammary glands

Milk production

(c) Simple neuroendocrine pathway

(b) Simple neurohormone pathway

(a) Simple endocrine pathway

Hypothalamus

Glycogen breakdown, glucose release into blood

Figure 45.2a–c