CoverModule 1.0. Homeostasis, Membranes, Electrophysiology and ANS1.1. Homeostasis1.1.1. Homeostasis Defined1.1.2. Homeostatic Control Systems1.1.3. Feedback Response Loop1.2. Cell Transport; Water & Solutes1.2.1. Fluid Compartments1.2.2. Osmosis1.2.3. Diffusion of Solutes1.2.4. Active Transport1.2.5. Bulk Transport1.3. Electrophysiology1.3.1. Ions and Cell Membranes1.3.2. Membrane Potentials1.3.3. Graded Potential1.3.4. Action Potentials1.3.5. Refractory Periods1.3.6. Propagation of an Action Potential1.4. The Synapse1.5. The Autonomic Nervous System1.5.1. Organization of the Nervous System1.5.2. Structural Organization of the ANS1.5.3. The SNS and the PNS1.5.4. The Enteric Nervous System1.5.5. Physiology of the ANS1.5.6. Neurotransmitters of the ANS1.5.7. Receptors of the ANS1.5.8. Actions of the Autonomic Nervous System1.5.9. Table of Actions for the SNS and PNS and Some Common DrugsModule 2.0. Skeletal Muscle and Special Senses2.1. Structural Organization of Skeletal Muscle2.2.1. Neuromuscular Junction, Excitation-Contraction Coupling2.2.2. Muscle Contractures and Cramps2.3. Whole Muscle Contraction, Fiber Type, Fatigue and Muscle Pharmacology2.3.1. Motor Units2.3.2. Factors that Influence the Force of Contraction2.3.2. Factors that Influence the Force of Muscle Contraction2.3.3. Energy Source for Muscle Contraction2.3.4. Skeletal Muscle Fiber Types2.3.5. Fatigue2.3.6. Muscle Pharmacology2.4. Smooth Muscle2.4.1. Smooth Muscle Contraction2.5. Control of Body Movement2.5.1. Voluntary Control of Muscle2.5.2. Reflexes2.6. Taste and Smell2.6.1. Taste2.6.2. The Sense of Smell2.7. Vision2.7.1. Structure of the Eye2.7.2. Focusing Light on the Retina2.7.3. Converting Light to Action Potentials2.7.4. The Retina2.7.5. Phototransduction2.7.6. Receptive Fields2.8. Hearing and Equilibrium2.8.1. The Nature of Sound2.8.2. The Hearing Apparatus2.8.3. Sound Vibrations to Action Potentials2.8.4. The Sense of Balance and EquilibriumModule 3.0. Cardiovascular System3.1. Structure of the Heart3.1.1. Chambers and Circulation3.2. Cardiac Cell Action Potentials3.2.1. Action Potentials in Cardiac Muscle Cells3.2.2. Action Potentials in Cardiac Autorhythmic cells3.2.3. Cellular Mechanisms of Inotropy and Chronotropy3.3. Electrophysiology of Heart Muscle3.3.1. Heart Conduction System3.3.2. Electrocardiogram (ECG)3.3.3. Abnormal ECG - Current of Injury3.4. The Cardiac Cycle3.4.1. Cardiac cycle3.4.2. Cardiac Measurements and Pressure Volume Loops3.5. Blood vessels and Blood Pressure3.5.1. Arteries and Veins3.5.2. Capillaries3.5.3. Blood Pressure Regulation and Shock3.5.4. Capillary Exchange3.5.5. Myogenic and Paracrine Regulation of Vasoconstriction and Vasodilation3.6. Blood3.6.1. Composition of Blood3.6.2. Hematopoeisis3.6.3. Breaking Down Red Blood Cells3.6.4. HemostasisModule 4.0. Urinary and Respiratory Systems4.1. Function and Structure of the Kidney4.1.1. Urinary System Function4.1.2. Functional Anatomy of the Urinary System4.1.3. The Nephron: Functional Unit of the Kidney4.1.4. The Renal Corpuscle: Bowman's Capsule4.2. Physiology of Urine Production4.2.1. Filtration4.2.2. Renal Clearance4.2.3. Tubular Reabsorption4.2.4. Urine Concentration and Dilution4.2.5. Hormonal Regulation of Urine Production4.3. Acid/Base Balance4.3.1. Buffers4.3.2. Acid/Base Disturbances4.4. The Respiratory System4.4.1. Respiratory System Structure and Function4.4.2. Respiratory Membrane4.4.3. Respiratory pressures and Inspriation/Expiration4.4.4. Alveoli and Surfactant4.4.5. Pneumothorax4.4.6. Pressure-Volume Loops and the Work of Breathing4.5. Gas Exchange and Transport4.5.1. Gas Laws4.5.2. Partial Pressure Gradients in the Lung4.5.3. Alveolar Gas Equation4.5.4. Oxygen and Carbon Dioxide Transport in the Blood4.5.5. Alveolar Ventilation4.5.6. Ventilation/Perfusion Ratio4.6. Chronic Bronchitis and Emphysema4.6.1. Respiratory Control by the Medulla Oblongata4.6.2. Chemicals that Regulate VentilationModule 5.0. Digestive, Endocrine and Reproductive Systems5.1. Functional Anatomy of the Digestive System5.1.1. Layers of the Digestive Tract5.1.2. Enteric Nervous System5.1.3. Organs of the Digestive System5.2. Digestion5.2.1. Carbohydrates5.2.2. Proteins5.2.3. Lipids5.2.4. Lipoproteins5.3. Regulation of Digestive Secretions5.4. Endocrine System5.4.1. Overview of the Endocrine System5.4.2. Hormone Receptors5.4.3. Hormones of the Body5.4.4. Other Hormones: Melatonin and Pheromones5.5. The Hypothalamus and Pituitary Gland5.5.1. Structure and Function of the Hypothalamus and Pituitary Gland5.5.2. The Posterior Pituitary5.5.3. The Anterior Pituitary5.5.4. Growth Hormone5.5.5. Prolactin5.5.6. Thyroid Hormones5.5.7. Adrenal Hormones5.6. Pancreas5.6.1. Insulin and Glucagon5.6.2. Diabetes Mellitus5.7. Reproductive System Anatomy5.7.1. Female Reproductive Anatomy5.7.2. Male Reproductive Anatomy5.7.3. Sexual Development at Puberty5.7.4. Male Reproductive Endocrine Axis5.7.5. Spermatogenesis5.7.6. Female Reproductive System: Oogenesis5.7.7. Ovulation and Fertilization5.7.8. The Ovarian Cycle5.7.9. The Uterine Cycle5.7.10. PregnancyAppendix A. GenderAppendix B. The Placebo EffectB.2.1. The Placebo EffectB.2.2. Examples of the Placebo EffectB.2.3. How do Placebos Work?B.2.4. Are Placebos Ethical?B.2.5. How do we validate actual effectiveness of placebosB.2.6. Tips for evaluating scientific evidenceB.2.7. What about Faith Healings
5.7.7

Ovulation and Fertilization

Ovulation is the event that releases the oocyte from the follicle. This event is under the control of LH. As we will discuss later, just prior to ovulation there is a sharp increase in the levels of LH. This increase is referred to as the LH surge and is the apparent trigger for the events of ovulation. The Graafian follicle moves to the surface of the ovary and appears like a small blister on the ovarian wall. Ovulation is achieved when this "blister" bursts and the oocyte, the follicular fluid, and the cumulus layer of granulosa cells is expelled from the follicle. The cumulus cells surrounding the oocyte at ovulation are called the corona radiata. The remaining granulosa cells and thecal cells of the follicle become the corpus luteum (luteum = yellow, corpus = body).  This change of the follicle to a corpus luteum is called luteinization and is brought about by the increase of luteinizing hormone (LH). The corpus luteum becomes the endocrine portion of the ovary and secretes estrogen and progesterone (described later). Progesterone is a hormone critical for establishing and maintaining pregnancy.  The progesterone levels secreted by the corpus luteum during pregnancy send negative feedback to the hypothalamus and pituitary gland to keep GnRH, LH and FSH secretions low so that no other dominant follicles develop while a woman is pregnant. 

If the oocyte is not fertilized, the corpus luteum survives about 10-12 days and then begins to degenerate becoming the corpus albicans (albicans – white). If the oocyte is fertilized, the corpus luteum is maintained throughout the first part of pregnancy, but later, the placenta will take over the job of producing estrogen and progesterone. After ovulation, the oocyte, along with its corona radiata, will enter the fallopian tubes.

Fertilization typically takes place in the ampulla (distal end) of the Fallopian tube. In order to penetrate the ovum, the sperm will have to negotiate their way through the corona radiata cells and the zona pellucida. Many sperm cells will die trying to do this and only one will ultimately be successful. Penetration of the sperm triggers completion of the 2nd meiotic division. The union of the sperm and the ovum forms a zygote (a fertilized egg).

image254.jpg
Fertilization.
By OpenStax College License: [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons Link: https://commons.wikimedia.org/wiki/File%3A2901_Sperm_Fertilization.jpg

While still in the Fallopian tube, the zygote begins the process of cell division, mitosis, and becomes an embryo. The embryo continues to grow by cell division as it travels towards the uterus. The fallopian tubes contain mucus secreting cells and ciliated cells. During the time of ovulation, high estrogen levels cause the cilia to beat more strongly toward the uterus.  High estrogen levels also create regular contractions, every 4-8 seconds, of the smooth muscle along the length of the fallopian tube resulting in a sweeping movement slowly moving the ovum toward the uterus. 

Implantation generally occurs on the endometrium at the superior end of the uterus, typically 6-7 days after fertilization. The image below shows the path of an oocyte after it has been ovulated.

An ectopic pregnancy is a rare situation that occurs if the fertilized ovum implants in a place other than the uterus, such as in the fallopian tube. Because the fallopian tube cannot expand to accommodate a growing baby, it could rupture leading to a life-threatening situation for the mother.  While the cause for a tubal pregnancy is not always known, there is an increased risk for an ectopic pregnancy if there is any damage to the fallopian tubes caused by pelvic inflammatory disease; lesions due to chlamydia infection or endometriosis; use of intrauterine devices or IUD for birth control; abdominal surgeries or intrauterine surgeries, including abortions or tubal ligation; or use of assisted reproductive technology, like IVF. Gratefully, 98% of the time there are no complications to the normal process of implantation of the ovum in the uterus after fertilization.

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