Unit 8 – Hormones & the Brain

What are the general principles of hormone actions?

Hormones are chemical messengers that often act slowly, last a long time, affect multiple tissues, and influence behavior.

How do hormones and behavior affect each other?

Hormones influence behavior, and behavior can change hormone levels.

What is the difference between endocrine, autocrine, and paracrine signaling?

Endocrine signals travel through blood to distant cells. Autocrine signals affect the same cell, and paracrine signals affect nearby cells.

What is the difference between allomones and pheromones?

Pheromones are chemical signals that affect the same species. Allomones affect different species.

Compare and contrast protein/peptide vs. steroid hormone actions.

Protein/peptide hormones bind to cell-surface receptors and act quickly. Steroid hormones enter cells and bind to internal receptors, acting more slowly.

How do protein/peptide hormones change the activity of receiving cells?

They activate second messengers: cAMP (cyclic adenosine monophosphate; carries signals), IP3 (inositol trisphosphate; releases calcium), and DAG (diacylglycerol; activates signaling proteins).

How do steroid hormones change the activity of receiving cells?

They change gene transcription, affecting which proteins are made. Their effects are slower and longer-lasting.

What is the hypothalamic-pituitary system?

The hypothalamus controls the pituitary gland, which regulates hormone release throughout the body.

What is the difference between the anterior and posterior pituitary?

The anterior pituitary makes and releases hormones. The posterior stores and releases hormones made by the hypothalamus.

How does the hypothalamus control the anterior pituitary?

It sends releasing hormones through the pituitary portal blood system to control hormone release.

What are releasing hormones and tropic hormones?

Releasing hormones control the anterior pituitary. Tropic hormones control other endocrine glands.

What is the HPA axis, and how are stress hormones released?

HPA (hypothalamic-pituitary-adrenal axis; stress-response system): The hypothalamus releases CRH (corticotropin-releasing hormone; triggers ACTH). The pituitary releases ACTH (adrenocorticotropic hormone; triggers cortisol), and the adrenal cortex releases cortisol.

How does negative feedback regulate the HPA axis?

High cortisol signals the hypothalamus and pituitary to release less CRH (triggers ACTH) and ACTH (triggers cortisol), reducing cortisol production.

What happens if anterior pituitary cells cannot respond to releasing hormones?

They release less hormone. For example, no response to CRH (triggers ACTH) causes less ACTH (triggers cortisol) and cortisol.

What happens if negative feedback in the HPA axis is blocked?

Blocked cortisol receptors prevent normal feedback. CRH and ACTH may stay high, causing excess cortisol.

How do cortisol and adrenaline differ during stress?

Cortisol from the adrenal cortex produces a longer-lasting stress response. Adrenaline from the adrenal medulla acts quickly.

How do sex chromosomes (XY or XX) determine production of sex hormones?

SRY (sex-determining region Y gene; triggers testes development) usually causes testes to form and produce testosterone. Without SRY, ovaries typically develop.

What is the HPG axis, and how does it regulate sex hormones?

HPG (hypothalamic-pituitary-gonadal axis; regulates reproduction): GnRH (gonadotropin-releasing hormone; triggers LH/FSH) stimulates LH (luteinizing hormone; sex hormone production) and FSH (follicle-stimulating hormone; egg/sperm development).

How do LH and FSH work in the testes?

LH (luteinizing hormone; stimulates testosterone) activates Leydig cells. FSH (follicle-stimulating hormone; supports sperm production) activates Sertoli cells.

How do LH and FSH regulate the menstrual cycle?

FSH (follicle-stimulating hormone; supports follicle growth) increases estrogen production. An LH (luteinizing hormone; triggers ovulation) surge releases an egg.

What are the four phases of the menstrual cycle?

Menstrual: the lining sheds. Follicular: estrogen rises. Ovulation: an egg is released. Luteal: progesterone rises.

How does exposure to androgens impact mammalian development?

Androgens, such as testosterone, promote masculinization of reproductive structures. Effects depend on hormone exposure and whether cells respond to androgens.

How can changes in chromosomes or hormone receptors affect sexual development?

XXY may reduce testosterone; XYY may increase growth. AIS (androgen insensitivity syndrome; poor androgen response), 5α-reductase deficiency (reduced DHT production), and CAH (congenital adrenal hyperplasia; excess prenatal androgens) alter development.

Describe the activational effects of gonadal steroids on mating behavior in female rodents.

Estrogen and progesterone activate brain circuits that help produce lordosis, the female mating posture.

What is the role of the VMH in female rodent mating?

VMH (ventromedial hypothalamus; controls female mating posture) responds to estrogen by increasing progesterone receptors and dendrite growth, helping trigger lordosis.

Describe the activational effects of gonadal steroids on mating behavior in male rodents.

Androgens activate brain circuits that support male mating behavior.

What is the role of the mPOA in male rodent mating?

mPOA (medial preoptic area; controls mating and ejaculation) contains steroid-sensitive neurons.

What is the role of the septal region in sexual behavior?

The septal region contributes to sexual arousal, pleasure, reward, and orgasm.

What is the function of oxytocin?

Oxytocin supports uterine contractions, milk release, social bonding, and orgasm.

What is the function of vasopressin?

Vasopressin, also called ADH (antidiuretic hormone; helps kidneys retain water), regulates blood pressure and supports social memory.

Where are oxytocin and vasopressin produced and stored?

Both are produced in the hypothalamus and stored and released by the posterior pituitary.

Describe the milk letdown pathway.

Suckling activates the hypothalamus, causing the posterior pituitary to release oxytocin. Oxytocin contracts mammary cells to release milk; continued suckling creates positive feedback.

What is the difference between negative and positive feedback loops?

Negative feedback reduces hormone release to maintain balance (e.g., high cortisol lowers CRH and ACTH). Positive feedback increases hormone release until a process ends (e.g., suckling increases oxytocin release).