Chapter 8: Hormones & Sex

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Testes

Produce sperm cells

Ovaries

Produce ova

Steroid hormones produced by both gonads

Androgens (Testosterone), Estrogens (Estradiol), Progestins (Progesterone)

Gonadotropin releasing hormone (GnRH)

Produced by hypothalamic neuroendocrine cells, secreted into the blood vessels and carried to the anterior pituitary via hypothalamic-pituitary portal system (see Neuroendocrine System: Regions)

Gonadotropins

Released by anterior pituitary following GnRH

Follicle Stimulating Hormone and Luteinizing Hormone

Drive the release of gonadal steroid hormones

Two major effects of sex hormones

Organizational (developmental) and activational

Organizational effects on gonads

Indifferent (primordial) gonads

Presence of a Y chromosome triggers the synthesis of SRY protein at about 6 weeks of development; allows growth of the medulla into the testes while the cortex shrinks away

Organizational effects on internal organs

At 6 weeks, zygote contains two precursor duct systems (Wolffian system and Müllerian system)

Once formed, fetal testes release testosterone and Müllerian-inhibiting hormone (8 weeks of gestation)

Wolffian system

One of the two precursor duct systems present zygote at 6 weeks

Potential to develop into epididymis, vas deferens, and seminal ducts

Müllerian system

One of the two precursor duct systems present zygote at 6 weeks

Potential to develop into fallopian tubes, uterus, and inner vagina

Male reproductive organ development

XY chromosome; Y chromosome being testis-determining factor

Primordial gonads develop into testes; anti-Müllerian hormone and androgens are produced

Defeminization and masculinization occur

Defeminization

Triggered by anti-Müllerian hormone

Müllerian system withers away

Masculinization

Triggered by androgens

Wolffian system develops into vas deferens, seminal vesicles, prostate

Primordial external genitalia develop into penis and scrotum

Female reproductive organ development

XX chromosome

Primordial gonads develop into ovaries; no hormones are produced

Müllerian system develops into fimbriae, fallopian tubes, uterus, inner vagina

Wolffian system, without androgens, withers away

Primordial external genitalia develop into clitoris, labia, outer vagina

Activational effects

Puberty, a time period during which fertility is achieved, growth spurt occurs, and secondary sex characteristics develop; marked by surge in hormone release from the anterior pituitary

Pituitary

Anterior and posterior

Hypothalamus

Supraoptic and paraventricular

Posterior pituitary

Major hormones (Vasopressin and Oxytocin) signaled via neural connections and released into the blood; negative feedback signaling

Controls the secretion of anterior pituitary hormones via its own set of hormones; releasing and inhibitory factors

Vasopressin

Facilitates water reabsorption in the kidney

Oxytocin

Parental behavior

Releasing factors

Stimulate the release of an anterior pituitary hormone

Inhibitory Factors

Inhibit the release of an anterior pituitary hormone

Anterior pituitary

Considered to be the master gland because it releases tropic hormones

Part of the hypothalamic-pituitary portal system

Releases gonadotropins (see Neuroendocrine System: Gonads)

Hypothalamic-pituitary portal system

Carries GnRH from the hypothalamus to the anterior pituitary (see Neuroendocrine System: Gonads)

Tropic hormones

Primary function is to influence the release of other hormones

Prolactin, gonadotropic hormones (FSH and LH), thyroid-stimulating hormone, ACTH, growth hormone

Neuroendocrine cells

Special category of cell

Hormones

Chemicals released by endocrine glands into blood circulation

Act on target tissues throughout the body (including the brain) to produce physiological effects

Three main categories of hormones

Peptides, Amines, Steroids

Peptide hormones

Small protein molecules made of a string of amino acids

Bind to receptor proteins on the surface; activate second messengers; fast, but not as fast as synaptic signals

Amine hormones

Modified versions of single amino acids; smaller and simpler

Bind to receptor proteins on the surface; activate second messengers; fast, but not as fast as synaptic signals

Steroid hormones

Derived from cholesterol; most important for sexual development and behavior

Bind to receptors inside the target cell; binds to DNA and controls expression of other genes

Hypothalamus

Control of hormone secretions

Pineal gland

Reproductive maturation; body rhythms

Anterior pituitary gland

Part of the pituitary gland

Hormone secretion by thyroid, adrenal cortex, and gonads; growth

Posterior pituitary gland

Part of the pituitary gland

Water balance; salt balance

Thyroid

Growth and development; metabolic rate

Adrenal cortex (outer bark)

Part of the adrenal glands

Salt and carbohydrate metabolism, inflammatory reactions

Adrenal medulla (inner core)

Part of the adrenal glands

Emotional arousal (epinephrine)

Pancreas

Sugar metabolism

Gut

Digestion and appetite control

Gonads (testes/ovaries)

Body development; maintenance of reproductive organs in adults