Ap Bio Reading Guide Chapter 9 Cell Cycle

March 03, 2022 Post a Comment

Pinnacle things to know

The menstrual bicycle starts with the showtime twenty-four hour period of the period and ends when the next period begins
Hormone signals are sent back and forth between the brain and the ovaries
The first role of the bike prepares an egg to be released from the ovary, and builds the lining of the uterus
The second part of the cycle prepares the uterus and torso to take a fertilized egg, or to commencement the next cycle if pregnancy doesn't happen

The menstrual bike is more than just the period. In fact, the menstruum is only the first phase of the cycle. The menstrual bicycle is actually made up of two cycles that interact and overlap—one happening in the ovaries and one in the uterus. The brain, ovaries, and uterus work together and communicate through hormones (chemic signals sent through the blood from ane role of the body to another) to proceed the wheel going.

A menstrual cycle starts with the first solar day of the period and ends with the start of the next menstruum. An entire menstrual wheel commonly lasts between 24 and 38 days (i), but the length may vary from cycle to cycle, and may also alter over the years. Cycle length changes betwixt menarche (when periods first beginning during puberty) and menopause (when periods cease permanently) (two,3).

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Understanding the menstrual bike is important because information technology tin bear upon the body from head to toe.

Some people observe changes in their pilus, pare, poop, chronic disease symptoms, mental health, migraine headaches, or the manner they experience sexual activity at different points in the menstrual cycle. Information technology's besides the body'south way of preparing for pregnancy over and over again, then people having penis-in-vagina sex (the kind of sex you can become significant from) may want to pay attention to the menstrual bike. Hormonal methods of nativity control forbid some or all of the steps in the cycle from happening, which keeps pregnancy from occurring.

Read on for the breakdown of each phase of the cycle and what is happening in the uterus and in the ovaries.

An overview:

Menses: The period—the shedding of the uterine lining. Levels of estrogen and progesterone are low.
The follicular stage: The time between the offset solar day of the menstruum and ovulation. Estrogen rises equally an egg prepares to be released.
The proliferative phase: After the period, the uterine lining builds dorsum up again.
Ovulation: The release of the egg from the ovary, mid-cycle. Estrogen peaks just beforehand, and and then drops shortly later on.
The luteal phase: The time between ovulation and earlier the start of menstruation, when the trunk prepares for a possible pregnancy. Progesterone is produced, peaks, and and so drops.
The secretory phase: The uterine lining produces chemicals that volition either assistance support an early pregnancy or will prepare the lining to break downward and shed if pregnancy doesn't occur.

Act 1: The first part of the cycle

Uterus: Catamenia

When: From the time bleeding starts to the time information technology ends.

What: Old blood and tissue from inside the uterus is shed through the vagina.

Each menstrual bicycle starts with flow (the period). A period is the normal shedding of blood and endometrium (the lining of the uterus) through the cervix and vagina. A normal flow may last up to viii days (ane), simply on boilerplate lasts about 5 or 6 (iv).

Ovaries: Follicular phase

When: From the start of the period until ovulation.

What: Signals from the brain tell the ovaries to fix an egg that will exist released.

During the menstruation, the pituitary gland (a pocket-size area at the base of the brain that makes hormones) produces a hormone chosen follicle stimulating hormone (FSH). FSH tells the ovaries to prepare an egg for ovulation (release of an egg from the ovary). Throughout the menstrual bike, in that location are multiple follicles (fluid filled sacs containing eggs) in each ovary at dissimilar stages of development (v,six). About halfway through the follicular stage (but as the menses is ending) one follicle in ane of the ovaries is the largest of all the follicles at nearly 1 cm (0.iv in) (6,7). This follicle becomes the dominant follicle and is the one prepared to be released at ovulation. The ascendant follicle produces estrogen as information technology grows (viii), which peaks just before ovulation happens (7). For most people, the follicular phase lasts x-22 days, simply this can vary from bike-to-bicycle (4).

Uterus: Proliferative phase

When: From the cease of the period until ovulation.

What: The uterus builds up a thick inner lining.

While the ovaries are working on developing the egg-containing follicles, the uterus is responding to the estrogen produced by the follicles, rebuilding the lining that was just shed during the terminal menses. This is called the proliferative phase because the endometrium (the lining of the uterus) becomes thicker. The endometrium is thinnest during the period, and thickens throughout this stage until ovulation occurs (9). The uterus does this to create a identify where a potential fertilized egg tin can implant and abound (x).

Interlude: Ovulation

When: About midway through the cycle, but this tin can change cycle-to-cycle. Ovulation divides the ii phases of the ovarian bicycle (the follicular phase and the luteal phase).

What: An egg is released from the ovary into the fallopian tube.

The dominant follicle in the ovary produces more and more estrogen as information technology grows larger. The dominant follicle reaches well-nigh two cm (0.viii in)—just can be up to 3 cm—at its largest right earlier ovulation (6,seven). When estrogen levels are high plenty, they signal to the brain causing a dramatic increase in luteinizing hormone (LH) (11). This spike is what causes ovulation (release of the egg from the ovary) to occur. Ovulation commonly happens well-nigh 13-15 days before the start of the side by side menses (12).

Act 2: The second part of the cycle

Ovary: Luteal Phase

When: From ovulation until the start of the adjacent period.

What: The sac that contained the egg produces estrogen and progesterone.

Once ovulation occurs, the follicle that independent the egg transforms into something called a corpus luteum and begins to produce progesterone as well as estrogen (10,xiii). Progesterone levels acme virtually halfway through this phase (fourteen). The hormonal changes of the luteal phase are associated with common premenstrual symptoms that many people experience, such as mood changes, headaches, acne, bloating, and breast tenderness.

If an egg is fertilized, progesterone from the corpus luteum supports the early on pregnancy (15). If no fertilization occurs, the corpus luteum will offset to break down between 9 and 11 days subsequently ovulation (10). This results in a driblet in estrogen and progesterone levels, which causes period. The luteal phase typically lasts nigh fourteen days, but between 9 and sixteen days is common (iv,12).

Uterus: Secretory Phase

When: From ovulation until the kickoff of the next menstruum.

What: The lining of the uterus releases or secretes chemicals that will either help an early pregnancy adhere if an egg was fertilized, or assist the lining break downwardly and shed if no egg was fertilized.

During this stage, the endometrium prepares to either support a pregnancy or to interruption down for menstruum. Rising levels of progesterone crusade the endometrium to stop thickening and to offset preparing for the potential attachment of a fertilized egg. The secretory stage gets its name because the endometrium is secreting (producing and releasing) many types of chemic messengers. The near notable of these messengers are the prostaglandins, which are secreted by endometrial cells and cause changes to other cells nearby.

Two prostaglandins in particular chosen, "PGF2α" and "PGE2", cause the uterine muscle to contract (cramp). The amounts of these prostaglandins rising afterward ovulation and reach their peak during period (16,17). The cramping caused past this prostaglandin helps trigger the period. If a pregnancy occurs, prostaglandin production is inhibited (eighteen) and so that these contractions won't bear upon an early on pregnancy. If pregnancy does not occur, the corpus luteum stops producing estrogen and progesterone. The drop in hormones, along with the effects of the prostaglandins, cause the blood vessels to constrict (tighten) and tissue of the endometrium to break downwardly (10).